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1794 lines
52 KiB
HTML
1794 lines
52 KiB
HTML
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<title>LuaBridge 2.0 Reference Manual</title>
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<!--=========================================================================-->
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<body>
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<header>
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<hr>
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<h1>LuaBridge 2.0 Reference Manual</h1>
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<hr>
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</header>
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<small>
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Official repository is located at
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<a href="https://github.com/vinniefalco/LuaBridge">https://github.com/vinniefalco/LuaBridge</a>.
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<br>
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Copyright © 2012 Vinnie Falco. Freely available under the terms of the
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<A HREF="http://www.opensource.org/licenses/mit-license.html">MIT License</A>.
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</small>
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<nav>
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<H2>Contents</H2>
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<UL id="toc" style="padding: 0">
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<LI><A href="#s1">1 - Introduction</A>
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<UL>
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<LI><A href="#s1.1">1.1 - Design</A>
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<LI><A href="#s1.2">1.2 - Repository</A>
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<LI><A href="#s1.3">1.3 - License and Credits</A>
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</UL>
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<P>
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<LI><A href="#s2">2 - Accessing C++ from Lua</A>
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<UL>
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<LI><A href="#s2.1">2.1 - Namespaces</A>
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<LI><A href="#s2.2">2.2 - Data, Properties, Functions, and CFunctions</A>
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<LI><A href="#s2.3">2.3 - Class Objects</A>
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<LI><A href="#s2.4">2.4 - Property Member Proxies</A>
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<LI><A href="#s2.5">2.5 - Constructors</A>
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<LI><A href="#s2.6">2.6 - Lua Stack</A>
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<LI><A href="#s2.7">2.7 - lua_State</A>
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</UL>
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<p>
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<LI><A href="#s3">3 - Passing Objects</A>
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<UL>
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<LI><A href="#s3.1">3.1 - C++ Lifetime</A>
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<LI><A href="#s3.2">3.2 - Lua Lifetime</A>
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<LI><A href="#s3.3">3.3 - Pointers, References, and Pass by Value</A>
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<LI><A href="#s3.4">3.4 - Shared Lifetime</A>
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<UL>
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<LI><A href="#s3.4.1">3.4.1 - Class RefCountedObjectPtr</A>
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<LI><A href="#s3.4.2">3.4.2 - Class RefCountedPtr</A>
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<LI><A href="#s3.4.3">3.4.3 - User-defined Containers</A>
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<LI><A href="#s3.4.4">3.4.4 - Container Constructors</A>
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</UL>
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<LI><A href="#s3.5">3.5 - Mixing Lifetimes</A>
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<LI><A href="#s3.6">3.6 - Convenience Functions</A>
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</UL>
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<P>
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<LI><A href="#s4">4 - Accessing Lua from C++</A>
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<UL>
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<LI><A href="#s4.1">4.1 - Class LuaRef</A>
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<UL>
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<LI><A href="#s4.1.1">4.1.1 - Type Conversions</A>
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<LI><A href="#s4.1.2">4.1.2 - Visual Studio 2010, 2012</A>
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</UL>
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<LI><A href="#s4.2">4.2 - Table Proxies</A>
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<LI><A href="#s4.3">4.3 - Calling Lua</A>
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<UL>
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<LI><A href="#s4.3.1">4.3.1 - Class LuaException</A>
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</UL>
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</uL>
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<P>
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<LI><A href="#s5">5 - Security</A>
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</UL>
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</nav>
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<!--========================================================================-->
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<section>
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<h1>1 - <span id="s1">Introduction</span></h1>
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<p>
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<a href="https://github.com/vinniefalco/LuaBridge">LuaBridge</a> is a
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lightweight and dependency-free library for mapping data, functions, and
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classes back and forth between C++ and <a href="http://wwww.lua.org">Lua</a>,
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a powerful, fast, lightweight, embeddable scripting language. LuaBridge has
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been tested and works with Lua revisions starting from 5.1.5, although it
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should work in any version of Lua from 5.1.0 and later. It also works
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transparently with <a href="http://luajit.org/">LuaJIT</a>.
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</p>
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<p>
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LuaBridge offers the following features:
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</p>
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<ul class="bullets" title="Features">
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<li><a href="http://www.opensource.org/licenses/mit-license.html">MIT Licensed</a>, no usage restrictions!</li>
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<li>Headers-only: No Makefile, no .cpp files, just one <code>#include</code>!</li>
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<li>Simple, light, and nothing else needed (like Boost).</li>
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<li>No macros, settings, or configuration scripts needed.</li>
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<li>Supports different object lifetime management models.</li>
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<li>Convenient, type-safe access to the Lua stack.</li>
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<li>Automatic function parameter type binding.</li>
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<li>Easy access to Lua objects like tables and functions.</li>
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<li>Written in a clear and easy to debug style.</li>
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<li>Does not require C++11.</li>
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</ul>
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<p>
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LuaBridge is distributed as a a collection of header files. You simply add
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one line, <code>#include "LuaBridge/LuaBridge.h"</code> where you want to
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pass functions, classes, and variables back and forth between C++ and Lua.
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There are no additional source files, no compilation settings, and no
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Makefiles or IDE-specific project files. LuaBridge is easy to integrate.
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</p>
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<p>
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C++ concepts like variables and classes are made available to Lua through a
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process called <em>registration</em>. Because Lua is weakly typed, the resulting
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structure is not rigid. The API is based on C++ template metaprogramming. It
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contains template code to automatically generate at compile-time the various
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Lua C API calls necessary to export your program's classes and functions to
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the Lua environment.
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</p>
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<p>
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To expose Lua objects to C++, a class called <code>LuaRef</code> is provided.
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The implementation allows C++ code to access Lua objects such as numbers
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or strings, but more importantly to access things like tables and their
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values. Using this class makes idioms like calling Lua functions simple
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and clean.
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</p>
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<!--========================================================================-->
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<section>
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<h2>1.1 - <span id="s1.1">Design</span></h2>
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<p>
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LuaBridge tries to be efficient as possible when creating the "glue" that
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exposes C++ data and functions to Lua. At the same time, the code was
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written with the intention that it is all as simple and clear as possible,
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without resorting to obscure C++ idioms, ugly preprocessor macros, or
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configuration settings. Furthermore, it is designed to be "header-only",
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making it very easy to integrate into your projects.
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</p>
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<p>
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Because LuaBridge was written with simplicity in mind there are some features
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that are not available. Although it comes close to the highest possible
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performance, LuaBridge is not quite the fastest,
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<a href="http://code.google.com/p/oolua/">OOLua</a> slightly outperforms
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LuaBridge in some tests. LuaBridge also does not try to implement every
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possible feature,
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<a href="http://www.rasterbar.com/products/luabind.html">LuaBind</a>
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explores every corner of the C++ language (but it requires Boost).
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</p>
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<p>
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LuaBridge does not support:
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</p>
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<ul class="bullets">
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<li>Enumerated constants
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<li>More than 8 parameters on a function or method (although this can be
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increased by adding more <code>TypeListValues</code> specializations).
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<li>Overloaded functions, methods, or constructors.
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<li>Global variables (variables must be wrapped in a named scope).
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<li>Automatic conversion between STL container types and Lua tables.
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<li>Inheriting Lua classes from C++ classes.
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<li>Passing nil to a C++ function that expects a pointer or reference.
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<li>Standard containers like <code>std::shared_ptr</code>.
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</ul>
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</section>
|
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<!--========================================================================-->
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<section>
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<h2>1.2 - <span id="s1.2">Repository</span></h2>
|
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<p>
|
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The official repository is located at
|
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<a href="https://github.com/vinniefalco/LuaBridge">https://github.com/vinniefalco/LuaBridge</a>.
|
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The branches are organized as follows:
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</p>
|
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<table>
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<tr>
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<td><b>master</b></td>
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<td>Tagged, stable release versions.</td>
|
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</tr>
|
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<tr>
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<td><b>release</b></td>
|
|
<td>A temporarily created branch that holds a release candidate for review.</td>
|
|
</tr>
|
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<tr>
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<td><b>develop</b></td>
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<td>Contains work in progress, possibly unfinished or with bugs.</td>
|
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</tr>
|
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</table>
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<p>
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These repositories are also available:
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</p>
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<table>
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<tr>
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<td><b><a href="https://github.com/vinniefalco/LuaBridgeUnitTests">LuaBridgeUnitTests</a></b></td>
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<td>A stand alone command line application to exercise LuaBridge functionality.</td>
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</tr>
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<tr>
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<td><b><a href="https://github.com/vinniefalco/LuaBridgeDemo">LuaBridgeUnitDemo</a></b></td>
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<td>A stand alone GUI application that provides an interactive console.</td>
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</tr>
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</table>
|
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</section>
|
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<!--========================================================================-->
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<section>
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<h2>1.3 - <span id="s1.3">License and Credits</span></h2>
|
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<p>
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LuaBridge is published under the terms of the
|
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<a href="http://www.opensource.org/licenses/mit-license.html">MIT License</a>:
|
|
</p>
|
|
|
|
<pre>
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Permission is hereby granted, free of charge, to any person obtaining a copy
|
|
of this software and associated documentation files (the "Software"), to deal
|
|
in the Software without restriction, including without limitation the rights
|
|
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
|
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copies of the Software, and to permit persons to whom the Software is
|
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furnished to do so, subject to the following conditions:
|
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The above copyright notice and this permission notice shall be included in
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all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
|
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
|
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
|
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SOFTWARE.
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</pre>
|
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<p>
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The original version of LuaBridge was written by Nathan Reed. The project
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has been taken over by Vinnie Falco, who added new functionality and wrote
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the new documentation. Vinnie also incorporated <code>LuaRef</code> and
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other Lua to C++ binding contributions from Nigel Atkinson.
|
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</p>
|
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<p>
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For questions, comments, or bug reports feel free to open a Github issue
|
|
or contact Vinnie Falco directly at the email address indicated below.
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</p>
|
|
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<ul>
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<li>Copyright 2012, Vinnie Falco <a href="mailto:vinnie.falco@gmail.com"><vinnie.falco@gmail.com></a>
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<li>Copyright 2008, Nigel Atkinson <a href="mailto:suprapilot+LuaCode@gmail.com"><suprapilot+LuaCode@gmail.com></a>
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<li>Copyright 2007, Nathan Reed
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<li>Portions from The Loki Library: Copyright 2001 by Andrei Alexandrescu
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|
</ul>
|
|
|
|
<p>
|
|
Older versions of LuaBridge up to and including 0.2 (available separately) are
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distributed under the BSD 3-Clause License. See the corresponding license file
|
|
in those versions (distributed separately) for more details.
|
|
</p>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
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</section>
|
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|
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<section>
|
|
|
|
<h1>2 - <span id="s2">Accessing C++ from Lua</span></h1>
|
|
|
|
<p>
|
|
In order to expose C++ data and functions to Lua, each piece of exported
|
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information must be <em>registered</em>. There are five types of objects that
|
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LuaBridge can register:
|
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</p>
|
|
|
|
<table>
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<tr>
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<td><b>Namespaces</b> </td>
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<td>A Lua table that contains other registrations.</td>
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</tr>
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<tr>
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<td><b>Data</b> </td>
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<td>Global or static variables, data members, and static data members.</td>
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</tr>
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<tr>
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<td><b>Functions </b></td>
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<td>Regular functions, member functions, and static member functions.</td>
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</tr>
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<tr>
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<td><b>CFunctions </b></td>
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<td>A regular function, member function, or static member function that
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uses the <code>lua_CFunction</code> calling convention.</td>
|
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</tr>
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<tr>
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<td><b>Properties </b></td>
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<td>Global properties, property members, and static property members.
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These appear like data to Lua, but are implemented in C++ using
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functions to get and set the values.</td>
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</tr>
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</table>
|
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<p>
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Both data and properties can be marked as <em>read-only</em> at the time of
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registration. This is different from <code>const</code>; the values of these
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objects can be modified on the C++ side, but Lua scripts cannot change them.
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Code samples that follow are in C++ or Lua, depending on context. For brevity
|
|
of exposition code samples in C++ assume the traditional variable
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<code>lua_State* L</code> is defined, and that a <code>using namespace luabridge</code>
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|
using-directive is in effect.
|
|
</p>
|
|
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|
<!--========================================================================-->
|
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<section>
|
|
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|
<h2>2.1 - <span id="s2.1">Namespaces</span></h2>
|
|
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<p>
|
|
All LuaBridge registrations take place in a <em>namespace</em>. When we refer
|
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to a <em>namespace</em> we are always talking about a namespace in the Lua
|
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sense, which is implemented using tables. The namespace need not correspond
|
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to a C++ namespace; in fact no C++ namespaces need to exist at all unless you
|
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want them to. LuaBridge namespaces are visible only to Lua scripts; they are
|
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used as a logical grouping tool. To obtain access to the global namespace
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we write:
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</p>
|
|
|
|
<pre>
|
|
getGlobalNamespace (L);
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</pre>
|
|
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<p>
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This returns an object on which further registrations can be performed. The
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subsequent registrations will go into the global namespace, a practice which
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is not recommended. Instead, we can add our own namespace by writing:
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</p>
|
|
|
|
<pre>
|
|
getGlobalNamespace (L)
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.beginNamespace ("test");
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</pre>
|
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<p>
|
|
This creates a table in <code>_G</code> called "test". Since we have not
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performed any registrations, this table will be empty except for some
|
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bookkeeping key/value pairs. LuaBridge reserves all identifiers that start
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with a double underscore. So <code>__test</code> would be an invalid name
|
|
(although LuaBridge will silently accept it). Functions like
|
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<code>beginNamespace</code> return the corresponding object on which we can
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make more registrations. Given:
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|
</p>
|
|
|
|
<pre>
|
|
getGlobalNamespace (L)
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.beginNamespace ("test")
|
|
.beginNamespace ("detail")
|
|
.endNamespace ()
|
|
.beginNamespace ("utility")
|
|
.endNamespace ()
|
|
.endNamespace ();
|
|
</pre>
|
|
|
|
<p>
|
|
The results are accessible to Lua as <code>test</code>, <code>test.detail</code>,
|
|
and <code>test.utility</code>. Here we introduce the <code>endNamespace</code>
|
|
function; it returns an object representing the original enclosing namespace.
|
|
All LuaBridge functions which create registrations return an object upon which
|
|
subsequent registrations can be made, allowing for an unlimited number of
|
|
registrations to be chained together using the dot operator. Adding two objects
|
|
with the same name, in the same namespace, results in undefined behavior
|
|
(although LuaBridge will silently accept it).
|
|
</p>
|
|
|
|
<p>
|
|
A namespace can be re-opened later to add more functions. This lets you split
|
|
up the registration between different source files. These are equivalent:
|
|
</p>
|
|
|
|
<pre>
|
|
getGlobalNamespace (L)
|
|
.beginNamespace ("test")
|
|
.addFunction ("foo", foo)
|
|
.endNamespace ();
|
|
|
|
getGlobalNamespace (L)
|
|
.beginNamespace ("test")
|
|
.addFunction ("bar", bar)
|
|
.endNamespace ();
|
|
</pre>
|
|
|
|
<p>
|
|
and
|
|
</p>
|
|
|
|
<pre>
|
|
getGlobalNamespace (L)
|
|
.beginNamespace ("test")
|
|
.addFunction ("foo", foo)
|
|
.addFunction ("bar", bar)
|
|
.endNamespace ();
|
|
</pre>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h2>2.2 - <span id="s2.2">Data, Properties, Functions, and CFunctions</span></h2>
|
|
|
|
<p>
|
|
These are registered into a namespace using <code>addVariable</code>,
|
|
<code>addProperty</code>, <code>addFunction</code>, and <code>addCFunction</code>.
|
|
When registered functions are called by scripts, LuaBridge automatically takes
|
|
care of the conversion of arguments into the appropriate data type when doing
|
|
so is possible. This automated system works for the function's return value,
|
|
and up to 8 parameters although more can be added by extending the templates.
|
|
Pointers, references, and objects of class type as parameters are treated
|
|
specially, and explained later. If we have:
|
|
</p>
|
|
|
|
<pre>
|
|
int globalVar;
|
|
static float staticVar;
|
|
|
|
std::string stringProperty;
|
|
std::string getString () { return stringProperty; }
|
|
void setString (std::string s) { stringProperty = s; }
|
|
|
|
int foo () { return 42; }
|
|
void bar (char const*) { }
|
|
int cFunc (lua_State* L) { return 0; }
|
|
</pre>
|
|
|
|
<p>
|
|
These are registered with:
|
|
</p>
|
|
|
|
<pre>
|
|
getGlobalNamespace (L)
|
|
.beginNamespace ("test")
|
|
.addVariable ("var1", &globalVar)
|
|
.addVariable ("var2", &staticVar, false) // read-only
|
|
.addProperty ("prop1", getString, setString)
|
|
.addProperty ("prop2", getString) // read only
|
|
.addFunction ("foo", foo)
|
|
.addFunction ("bar", bar)
|
|
.addCFunction ("cfunc", cFunc)
|
|
.endNamespace ();
|
|
</pre>
|
|
|
|
<p>
|
|
Variables can be marked <em>read-only</em> by passing <code>false</code> in
|
|
the second optional parameter. If the parameter is omitted, <em>true</em> is
|
|
used making the variable read/write. Properties are marked read-only by
|
|
omitting the set function. After the registrations above, the following Lua
|
|
identifiers are valid:
|
|
</p>
|
|
|
|
<pre>
|
|
test -- a namespace
|
|
test.var1 -- a lua_Number variable
|
|
test.var2 -- a read-only lua_Number variable
|
|
test.prop1 -- a lua_String property
|
|
test.prop2 -- a read-only lua_String property
|
|
test.foo -- a function returning a lua_Number
|
|
test.bar -- a function taking a lua_String as a parameter
|
|
test.cfunc -- a function with a variable argument list and multi-return
|
|
</pre>
|
|
|
|
<p>
|
|
Note that <code>test.prop1</code> and `test.prop2` both refer to the
|
|
same value. However, since <code>test.prop2</code> is read-only, assignment
|
|
attempts will generate a run-time error. These Lua statements have the stated effects:
|
|
</p>
|
|
|
|
<pre>
|
|
test.var1 = 5 -- okay
|
|
test.var2 = 6 -- error: var2 is not writable
|
|
test.prop1 = "Hello" -- okay
|
|
test.prop1 = 68 -- okay, Lua converts the number to a string.
|
|
test.prop2 = "bar" -- error: prop2 is not writable
|
|
|
|
test.foo () -- calls foo and discards the return value
|
|
test.var1 = foo () -- calls foo and stores the result in var1
|
|
test.bar ("Employee") -- calls bar with a string
|
|
test.bar (test) -- error: bar expects a string not a table
|
|
</pre>
|
|
|
|
<p>
|
|
LuaBridge does not support overloaded functions nor is it likely to in the
|
|
future. Since Lua is dynamically typed, any system that tries to resolve a set
|
|
of parameters passed from a script will face considerable ambiguity when
|
|
trying to choose an appropriately matching C++ function signature.
|
|
</p>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h2>2.3 - <span id="s2.3">Class Objects</span></h2>
|
|
|
|
<p>
|
|
A class registration is opened using either <code>beginClass</code> or
|
|
<code>deriveClass</code> and ended using <code>endClass</code>. Once
|
|
registered, a class can later be re-opened for more registrations using
|
|
<code>beginClass</code>. However, <code>deriveClass</code> should only be
|
|
used once. To add more registrations to an already registered derived class,
|
|
use <code>beginClass</code> on it. These declarations:
|
|
</p>
|
|
|
|
<pre>
|
|
struct A {
|
|
static int staticData;
|
|
static float staticProperty;
|
|
|
|
static float getStaticProperty () { return staticProperty; }
|
|
static void setStaticProperty (float f) { staticProperty = f; }
|
|
static void staticFunc () { }
|
|
|
|
static int staticCFunc () { return 0; }
|
|
|
|
std::string dataMember;
|
|
|
|
char dataProperty;
|
|
char getProperty () const { return dataProperty; }
|
|
void setProperty (char v) { dataProperty = v; }
|
|
|
|
void func1 () { }
|
|
virtual void virtualFunc () { }
|
|
|
|
int cfunc (lua_State* L) { return 0; }
|
|
};
|
|
|
|
struct B : public A {
|
|
double dataMember2;
|
|
|
|
void func1 () { }
|
|
void func2 () { }
|
|
void virtualFunc () { }
|
|
};
|
|
|
|
int A::staticData;
|
|
float A::staticProperty;
|
|
</pre>
|
|
|
|
<p>
|
|
are registered using:
|
|
</p>
|
|
|
|
<pre>
|
|
getGlobalNamespace (L)
|
|
.beginNamespace ("test")
|
|
.beginClass <A> ("A")
|
|
.addStaticData ("staticData", &A::staticData)
|
|
.addStaticProperty ("staticProperty", &A::staticProperty)
|
|
.addStaticFunction ("staticFunc", &A::staticFunc)
|
|
.addStaticCFunction ("staticCFunc", &A::staticCFunc)
|
|
.addData ("data", &A::dataMember)
|
|
.addProperty ("prop", &A::getProperty, &A::setProperty)
|
|
.addFunction ("func1", &A::func1)
|
|
.addFunction ("virtualFunc", &A::virtualFunc)
|
|
.addCFunction ("cfunc", &A::cfunc)
|
|
.endClass ()
|
|
.deriveClass <B, A> ("B")
|
|
.addData ("data", &B::dataMember2)
|
|
.addFunction ("func1", &B::func1)
|
|
.addFunction ("func2", &B::func2)
|
|
.endClass ()
|
|
.endNameSpace ();
|
|
</pre>
|
|
|
|
<p>
|
|
Method registration works just like function registration. Virtual methods
|
|
work normally; no special syntax is needed. const methods are detected and
|
|
const-correctness is enforced, so if a function returns a const object (or
|
|
a container holding to a const object) to Lua, that reference to the object
|
|
will be considered const and only const methods can be called on it.
|
|
Destructors are registered automatically for each class.
|
|
</p>
|
|
|
|
<p>
|
|
As with regular variables and properties, class data and properties can be
|
|
marked read-only by passing false in the second parameter, or omitting the set
|
|
set function respectively. The `deriveClass` takes two template arguments: the
|
|
class to be registered, and its base class. Inherited methods do not have to
|
|
be re-declared and will function normally in Lua. If a class has a base class
|
|
that is **not** registered with Lua, there is no need to declare it as a
|
|
subclass.
|
|
</p>
|
|
|
|
<p>
|
|
Remember that in Lua, the colon operator '<code>:</code>' is used for
|
|
method call syntax:
|
|
</p>
|
|
|
|
<pre>
|
|
local a = A ()
|
|
|
|
a.func1 () -- Does nothing
|
|
a:func1 () -- Works
|
|
</pre>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h2>2.4 - <span id="s2.4">Property Member Proxies</span></h2>
|
|
|
|
<p>
|
|
Sometimes when registering a class which comes from a third party library, the
|
|
data is not exposed in a way that can be expressed as a pointer to member,
|
|
there are no get or set functions, or the get and set functons do not have the
|
|
right function signature. Since the class declaration is closed for changes,
|
|
LuaBridge allows for a <em>property member proxy</em>. This is a pair of get
|
|
and set flat functions which take as their first parameter a pointer to
|
|
the object. This is easily understood with the following example:
|
|
</p>
|
|
|
|
<pre>
|
|
// Third party declaration, can't be changed
|
|
struct Vec
|
|
{
|
|
float coord [3];
|
|
};
|
|
</pre>
|
|
|
|
<p>
|
|
Taking the address of an array element, e.g. <code>&Vec::coord [0]</code>
|
|
results in an error instead of a pointer-to-member. The class is closed for
|
|
modifications, but we want to export Vec objects to Lua using the familiar
|
|
object notation. To do this, first we add a "helper" class:
|
|
</p>
|
|
|
|
<pre>
|
|
struct VecHelper
|
|
{
|
|
template <unsigned index>
|
|
static float get (Vec const* vec)
|
|
{
|
|
return vec->coord [index];
|
|
}
|
|
|
|
template <unsigned index>
|
|
static void set (Vec* vec, float value)
|
|
{
|
|
vec->coord [index] = value;
|
|
}
|
|
};
|
|
</pre>
|
|
|
|
<p>
|
|
This helper class is only used to provide property member proxies.
|
|
<code>Vec</code> continues to be used in the C++ code as it was before.
|
|
Now we can register the <code>Vec</code> class with property member proxies for
|
|
<code>x</code>, <code>y</code>, and <code>z</code>:
|
|
</p>
|
|
|
|
<pre>
|
|
getGlobalNamespace (L)
|
|
.beginNamespace ("test")
|
|
.beginClass <Vec> ("Vec")
|
|
.addProperty ("x", &VecHelper::get <0>, &VecHelper::set <0>)
|
|
.addProperty ("y", &VecHelper::get <1>, &VecHelper::set <1>)
|
|
.addProperty ("z", &VecHelper::get <2>, &VecHelper::set <2>)
|
|
.endClass ()
|
|
.endNamespace ();
|
|
</pre>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h2>2.5 - <span id="s2.5">Constructors</span></h2>
|
|
|
|
<p>
|
|
A single constructor may be added for a class using <code>addConstructor</code>.
|
|
LuaBridge cannot automatically determine the number and types of constructor
|
|
parameters like it can for functions and methods, so you must provide them.
|
|
This is done by specifying the signature of the desired constructor function
|
|
as the first template parameter to <code>addConstructor</code>. The parameter
|
|
types will be extracted from this (the return type is ignored). For example,
|
|
these statements register constructors for the given classes:
|
|
</p>
|
|
|
|
<pre>
|
|
struct A {
|
|
A ();
|
|
};
|
|
|
|
struct B {
|
|
explicit B (char const* s, int nChars);
|
|
};
|
|
|
|
getGlobalNamespace (L)
|
|
.beginNamespace ("test")
|
|
.beginClass <A> ("A")
|
|
.addConstructor <void (*) (void)> ()
|
|
.endClass ()
|
|
.beginClass <B> ("B")
|
|
.addConstructor <void (*) (char const*, int)> ()
|
|
.endClass ()
|
|
.endNamespace ();
|
|
</pre>
|
|
|
|
<p>
|
|
Constructors added in this fashion are called from Lua using the fully
|
|
qualified name of the class. This Lua code will create instances of
|
|
<code>A</code> and <code>B</code>.
|
|
</p>
|
|
|
|
<pre>
|
|
a = test.A () -- Create a new A.
|
|
b = test.B ("hello", 5) -- Create a new B.
|
|
b = test.B () -- Error: expected string in argument 1
|
|
</pre>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h2>2.6 - <span id="s2.6">Lua Stack</span></h2>
|
|
|
|
<p>
|
|
In the Lua C API, all operations on the <code>lua_State</code> are performed
|
|
through the Lua stack. In order to pass values back and forth between C++
|
|
and Lua, LuaBridge uses specializations of this template class concept:
|
|
</p>
|
|
|
|
<pre>
|
|
template <class T>
|
|
struct Stack
|
|
{
|
|
static void push (lua_State* L, T t);
|
|
static T get (lua_State* L, int index);
|
|
};
|
|
</pre>
|
|
|
|
<p>
|
|
When a specialization of <code>Stack</code> exists for a given type
|
|
<code>T</code> we say that the <code>T</code> is <em>convertible</em>.
|
|
Throughout this document and the LuaBridge API, these types can be used
|
|
anywhere a convertible type is expected.
|
|
</p>
|
|
|
|
<p>
|
|
The Stack template class specializations are used automatically for variables,
|
|
properties, data members, property members, function arguments and return
|
|
values. These basic types are supported:
|
|
</p>
|
|
|
|
<ul class="bullets">
|
|
<li><code>bool</code>
|
|
<li><code>char</code>, converted to a string of length one.
|
|
<li><code>char const*</code> and <code>std::string</code> strings.
|
|
<li>Integers, <code>float</code>, and <code>double</code>,
|
|
converted to <code>Lua_number</code>.
|
|
</ul>
|
|
|
|
<p>
|
|
User-defined types which are convertible to one of the basic types are
|
|
possible, simply provide a <code>Stack<></code> specialization in the
|
|
<code>luabridge</code> namespace for your user-defined type, modeled after
|
|
the existing types. For example, here is a specialization for a
|
|
<code>juce::String</code>:
|
|
</p>
|
|
|
|
<pre>
|
|
template <>
|
|
struct Stack <juce::String>
|
|
{
|
|
static void push (lua_State* L, juce::String s)
|
|
{
|
|
lua_pushstring (L, s.toUTF8 ());
|
|
}
|
|
|
|
static juce::String get (lua_State* L, int index)
|
|
{
|
|
return juce::String (luaL_checkstring (L, index));
|
|
}
|
|
};
|
|
</pre>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h2>2.7 - <span id="s2.7">lua_State</span></h2>
|
|
|
|
<p>
|
|
Sometimes it is convenient from within a bound function or member function
|
|
to gain access to the `lua_State*` normally available to a `lua_CFunction`.
|
|
With LuaBridge, all you need to do is add a `lua_State*` as the last
|
|
parameter of your bound function:
|
|
</p>
|
|
|
|
<pre>
|
|
void useState (lua_State* L);
|
|
|
|
getGlobalNamespace (L).addFunction ("useState", &useState);
|
|
</pre>
|
|
|
|
<p>
|
|
You can still include regular arguments while receiving the state:
|
|
</p>
|
|
|
|
<pre>
|
|
void useStateAndArgs (int i, std::string s, lua_State* L);
|
|
|
|
getGlobalNamespace (L).addFunction ("useStateAndArgs", &useStateAndArgs);
|
|
</pre>
|
|
|
|
<p>
|
|
When the script calls <code>useStateAndArgs</code>, it passes only the integer
|
|
and string parameters. LuaBridge takes care of inserting the <code>lua_State*</code>
|
|
into the argument list for the corresponding C++ function. This will work
|
|
correctly even for the state created by coroutines. Undefined behavior results
|
|
if the <code>lua_State*</code> is not the last parameter.
|
|
</p>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
</section>
|
|
|
|
<section>
|
|
|
|
<h1>3 - <span id="s3">Passing Objects</span></h1>
|
|
|
|
<p>
|
|
An object of a registered class <code>T</code> may be passed to Lua as:
|
|
</p>
|
|
|
|
<table>
|
|
<tr>
|
|
<td><b><code>T</code></b></td>
|
|
<td>Passed by value (a copy), with <em>Lua lifetime</em>.</td>
|
|
</tr>
|
|
<tr>
|
|
<td><b><code>T const</code></b></td>
|
|
<td>Passed by value (a copy), with <em>Lua lifetime</em>.</td>
|
|
</tr>
|
|
<tr>
|
|
<td><b><code>T*</code></b></td>
|
|
<td>Passed by reference, with <em>C++ lifetime</em>.</td>
|
|
</tr>
|
|
<tr>
|
|
<td><b><code>T&</code></b></td>
|
|
<td>Passed by reference, with <em>C++ lifetime</em>.</td>
|
|
</tr>
|
|
<tr>
|
|
<td><b><code>T const*</code></b></td>
|
|
<td>Passed by const reference, with <em>C++ lifetime</em>.</td>
|
|
</tr>
|
|
<tr>
|
|
<td><b><code>T const&</code></b></td>
|
|
<td>Passed by const reference, with <em>C++ lifetime</em>.</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h2>3.1 - <span id="s3.1">C++ Lifetime</span></h2>
|
|
|
|
<p>
|
|
The creation and deletion of objects with <em>C++ lifetime</em> is controlled by
|
|
the C++ code. Lua does nothing when it garbage collects a reference to such an
|
|
object. Specifically, the object's destructor is not called (since C++ owns
|
|
it). Care must be taken to ensure that objects with C++ lifetime are not
|
|
deleted while still being referenced by a <code>lua_State*</code>, or else
|
|
undefined behavior results. In the previous examples, an instance of <code>A</code>
|
|
can be passed to Lua with C++ lifetime, like this:
|
|
</p>
|
|
|
|
<pre>
|
|
A a;
|
|
|
|
push (L, &a); // pointer to 'a', C++ lifetime
|
|
lua_setglobal (L, "a");
|
|
|
|
push (L, (A const*)&a); // pointer to 'a const', C++ lifetime
|
|
lua_setglobal (L, "ac");
|
|
|
|
push <A const*> (L, &a); // equivalent to push (L, (A const*)&a)
|
|
lua_setglobal (L, "ac2");
|
|
|
|
push (L, new A); // compiles, but will leak memory
|
|
lua_setglobal (L, "ap");
|
|
</pre>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h2>3.2 - <span id="s3.2">Lua Lifetime</span></h2>
|
|
|
|
<p>
|
|
When an object of a registered class is passed by value to Lua, it will have
|
|
<em>Lua lifetime</em>. A copy of the passed object is constructed inside the
|
|
userdata. When Lua has no more references to the object, it becomes eligible
|
|
for garbage collection. When the userdata is collected, the destructor for
|
|
the class will be called on the object. Care must be taken to ensure that
|
|
objects with Lua lifetime are not accessed by C++ after they are garbage
|
|
collected, or else undefined behavior results. An instance of <code>B</code>
|
|
can be passed to Lua with Lua lifetime this way:
|
|
</p>
|
|
|
|
<pre>
|
|
B b;
|
|
|
|
push (L, b); // Copy of b passed, Lua lifetime.
|
|
lua_setglobal (L, "b");
|
|
</pre>
|
|
|
|
<p>
|
|
Given the previous code segments, these Lua statements are applicable:
|
|
</p>
|
|
|
|
<pre>
|
|
print (test.A.staticData) -- Prints the static data member.
|
|
print (test.A.staticProperty) -- Prints the static property member.
|
|
test.A.staticFunc () -- Calls the static method.
|
|
|
|
print (a.data) -- Prints the data member.
|
|
print (a.prop) -- Prints the property member.
|
|
a:func1 () -- Calls A::func1 ().
|
|
test.A.func1 (a) -- Equivalent to a:func1 ().
|
|
test.A.func1 ("hello") -- Error: "hello" is not a class A.
|
|
a:virtualFunc () -- Calls A::virtualFunc ().
|
|
|
|
print (b.data) -- Prints B::dataMember.
|
|
print (b.prop) -- Prints inherited property member.
|
|
b:func1 () -- Calls B::func1 ().
|
|
b:func2 () -- Calls B::func2 ().
|
|
test.B.func2 (a) -- Error: a is not a class B.
|
|
test.A.func1 (b) -- Calls A::func1 ().
|
|
b:virtualFunc () -- Calls B::virtualFunc ().
|
|
test.B.virtualFunc (b) -- Calls B::virtualFunc ().
|
|
test.A.virtualFunc (b) -- Calls B::virtualFunc ().
|
|
test.B.virtualFunc (a) -- Error: a is not a class B.
|
|
|
|
a = nil; collectgarbage () -- 'a' still exists in C++.
|
|
b = nil; collectgarbage () -- Lua calls ~B() on the copy of b.
|
|
</pre>
|
|
|
|
<p>
|
|
When Lua script creates an object of class type using a registered
|
|
constructor, the resulting value will have Lua lifetime. After Lua no longer
|
|
references the object, it becomes eligible for garbage collection. You can
|
|
still pass these to C++, either by reference or by value. If passed by
|
|
reference, the usual warnings apply about accessing the reference later,
|
|
after it has been garbage collected.
|
|
</p>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h2>3.3 - <span id="s3.3">Pointers, References, and Pass by Value</span></h2>
|
|
|
|
<p>
|
|
When C++ objects are passed from Lua back to C++ as arguments to functions,
|
|
or set as data members, LuaBridge does its best to automate the conversion.
|
|
Using the previous definitions, the following functions may be registered
|
|
to Lua:
|
|
</p>
|
|
|
|
<pre>
|
|
void func0 (A a);
|
|
void func1 (A* a);
|
|
void func2 (A const* a);
|
|
void func3 (A& a);
|
|
void func4 (A const& a);
|
|
</pre>
|
|
|
|
<p>
|
|
Executing this Lua code will have the prescribed effect:
|
|
</p>
|
|
|
|
<pre>
|
|
func0 (a) -- Passes a copy of a, using A's copy constructor.
|
|
func1 (a) -- Passes a pointer to a.
|
|
func2 (a) -- Passes a pointer to a const a.
|
|
func3 (a) -- Passes a reference to a.
|
|
func4 (a) -- Passes a reference to a const a.
|
|
</pre>
|
|
|
|
<p>
|
|
In the example above, all functions can read the data members and property
|
|
members of <code>a</code>, or call const member functions of <code>a</code>.
|
|
Only <code>func0</code>, <code>func1</code>, and <code>func3</code> can
|
|
modify the data members and data properties, or call non-const member
|
|
functions of <code>a</code>.
|
|
</p>
|
|
|
|
<p>
|
|
The usual C++ inheritance and pointer assignment rules apply. Given:
|
|
</p>
|
|
|
|
<pre>
|
|
void func5 (B b);
|
|
void func6 (B* b);
|
|
</pre>
|
|
|
|
<p>
|
|
These Lua statements hold:
|
|
</p>
|
|
|
|
<pre>
|
|
func5 (b) - Passes a copy of b, using B's copy constructor.
|
|
func6 (b) - Passes a pointer to b.
|
|
func6 (a) - Error: Pointer to B expected.
|
|
func1 (b) - Okay, b is a subclass of a.
|
|
</pre>
|
|
|
|
<p>
|
|
When a pointer or pointer to const is passed to Lua and the pointer is null
|
|
(zero), LuaBridge will pass Lua a `nil` instead. When Lua passes a
|
|
<code>nil</code> to C++ where a pointer is expected, a null (zero) is passed
|
|
instead. Attempting to pass a null pointer to a C++ function expecting a
|
|
reference results in <code>lua_error</code> being called.
|
|
</p>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h2>3.4 - <span id="s3.4">Shared Lifetime</span></h2>
|
|
|
|
<p>
|
|
LuaBridge supports a <em>shared lifetime</em> model: dynamically allocated
|
|
and reference counted objects whose ownership is shared by both Lua and C++.
|
|
The object remains in existence until there are no remaining C++ or Lua
|
|
references, and Lua performs its usual garbage collection cycle. A container
|
|
is recognized by a specialization of the <code>ContainerTraits</code>
|
|
template class. LuaBridge will automatically recognize when a data type is
|
|
a container when the correspoding specialization is present. Two styles of
|
|
containers come with LuaBridge, including the necessary specializations.
|
|
</p>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h3>3.4.1 - <span id="s3.4.1">Class RefCountedObjectPtr</span></h3>
|
|
|
|
<p>
|
|
This is an intrusive style container. Your existing class declaration must be
|
|
changed to be also derived from <code>RefCountedObject</code>. Given
|
|
<code>class T</code>, derived from <code>RefCountedObject</code>, the container
|
|
<code>RefCountedObjectPtr <T></code>` may be used. In order for
|
|
reference counts to be maintained properly, all C++ code must store a
|
|
container instead of the pointer. This is similar in style to
|
|
<code>std::shared_ptr</code> although there are slight differences. For
|
|
example:
|
|
</p>
|
|
|
|
<pre>
|
|
// A is reference counted.
|
|
struct A : public RefCountedObject
|
|
{
|
|
void foo () { }
|
|
};
|
|
|
|
struct B
|
|
{
|
|
RefCountedObjectPtr <A> a; // holds a reference to A
|
|
};
|
|
|
|
void bar (RefCountedObjectPtr <A> a)
|
|
{
|
|
a->foo ();
|
|
}
|
|
</pre>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h3>3.4.2 - <span id="s3.4.2">Class RefCountedPtr</span></h3>
|
|
|
|
<p>
|
|
This is a non intrusive reference counted pointer. The reference counts are
|
|
kept in a global hash table, which does incur a small performance penalty.
|
|
However, it does not require changing any already existing class declarations.
|
|
This is especially useful when the classes to be registered come from a third
|
|
party library and cannot be modified. To use it, simply wrap all pointers
|
|
to class objects with the container instead:
|
|
</p>
|
|
|
|
<pre>
|
|
struct A
|
|
{
|
|
void foo () { }
|
|
};
|
|
|
|
struct B
|
|
{
|
|
RefCountedPtr <A> a;
|
|
};
|
|
|
|
RefCountedPtr <A> createA ()
|
|
{
|
|
return new A;
|
|
}
|
|
|
|
void bar (RefCountedPtr <A> a)
|
|
{
|
|
a->foo ();
|
|
}
|
|
|
|
void callFoo ()
|
|
{
|
|
bar (createA ());
|
|
|
|
// The created A will be destroyed
|
|
// when we leave this scope
|
|
}
|
|
</pre>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h3>3.4.3 - <span id="s3.4.3">User-defined Containers</span></h3>
|
|
|
|
<p>
|
|
If you have your own container, you must provide a specialization of
|
|
<code>ContainerTraits</code> in the <code>luabridge</code> namespace for your
|
|
type before it will be recognized by LuaBridge (or else the code will not
|
|
compile):
|
|
</p>
|
|
|
|
<pre>
|
|
template <class T>
|
|
struct ContainerTraits <CustomContainer <T> >
|
|
{
|
|
typedef typename T Type;
|
|
|
|
static T* get (CustomContainer <T> const& c)
|
|
{
|
|
return c.getPointerToObject ();
|
|
}
|
|
};
|
|
</pre>
|
|
|
|
<p>
|
|
Standard containers like <code>std::shared_ptr</code> or
|
|
<code>boost::shared_ptr</code> <b>will not work</b>. This is because of type
|
|
erasure; when the object goes from C++ to Lua and back to C++, there is no
|
|
way to associate the object with the original container. The new container is
|
|
constructed from a pointer to the object instead of an existing container.
|
|
The result is undefined behavior since there are now two sets of reference
|
|
counts.
|
|
</p>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h3>3.4.4 - <span id="s3.4.4">Container Constructors</span></h3>
|
|
|
|
<p>
|
|
When a constructor is registered for a class, there is an additional
|
|
optional second template parameter describing the type of container to use.
|
|
If this parameter is specified, calls to the constructor will create the
|
|
object dynamically, via operator new, and place it a container of that
|
|
type. The container must have been previously specialized in
|
|
<code>ContainerTraits</code>, or else a compile error will result. This code
|
|
will register two objects, each using a constructor that creates an object
|
|
with Lua lifetime using the specified container:
|
|
</p>
|
|
|
|
<pre>
|
|
class C : public RefCountedObject
|
|
{
|
|
C () { }
|
|
};
|
|
|
|
class D
|
|
{
|
|
D () { }
|
|
};
|
|
|
|
getGlobalNamespace (L)
|
|
.beginNamespace ("test")
|
|
.beginClass <C> ("C")
|
|
.addConstructor <void (*) (void), RefCountedObjectPtr <C> > ()
|
|
.endClass ()
|
|
.beginClass <D> ("D")
|
|
.addConstructor <void (*) (void), RefCountedPtr <D> > ()
|
|
.endClass ();
|
|
.endNamespace ()
|
|
</pre>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
</section>
|
|
|
|
<section>
|
|
|
|
<h2>3.5 - <span id="s3.5">Mixing Lifetimes</span></h2>
|
|
|
|
<p>
|
|
Mixing object lifetime models is entirely possible, subject to the usual
|
|
caveats of holding references to objects which could get deleted. For
|
|
example, C++ can be called from Lua with a pointer to an object of class
|
|
type; the function can modify the object or call non-const data members.
|
|
These modifications are visible to Lua (since they both refer to the same
|
|
object). An object store in a container can be passed to a function expecting
|
|
a pointer. These conversion work seamlessly.
|
|
<p>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h2>3.6 - <span id="s3.6">Convenience Functions</span></h2>
|
|
|
|
<p>
|
|
The <code>setGlobal</code> function can be used to assign any convertible
|
|
value into a global variable.
|
|
</p>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
</section>
|
|
|
|
<section>
|
|
|
|
<h1>4 - <span id="s4">Accessing Lua from C++</span></h1>
|
|
|
|
<p>
|
|
Because Lua is a <em>dynamically typed language</em>, special consideration
|
|
is required to map values in Lua to C++. The following sections describe the
|
|
classes and functions used for representing Lua types. Only the essential
|
|
operations are explained; To gain understanding of all available functions,
|
|
please refer to the documentation comments in the corresponding source files.
|
|
</p>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h2>4.1 - <span id="s4.1">Class LuaRef</span></h2>
|
|
|
|
<p>
|
|
The <code>LuaRef</code> class is a container which references any Lua type.
|
|
It can hold anything which a Lua variable can hold: <strong>nil</strong>,
|
|
number, boolean, string, table, function, thread, userdata, and
|
|
lightuserdata. Because <code>LuaRef</code> uses the <code>Stack</code>
|
|
template specializations to do its work, classes, functions, and data
|
|
exported to Lua through namespace registrations can also be stored (these
|
|
are instances of userdata). In general, a <code>LuaRef</code> can represent
|
|
any <em>convertible</em> C++ type as well as all Lua types.
|
|
</p>
|
|
|
|
<p>
|
|
A <code>LuaRef</code> variable constructed with no parameters produces a
|
|
reference to <strong>nil</strong>:
|
|
</p>
|
|
|
|
<pre>
|
|
LuaRef v (L); // References nil
|
|
</pre>
|
|
|
|
<p>
|
|
To construct a <code>LuaRef</code> to a specific value, the two parameter
|
|
constructor is used:
|
|
</p>
|
|
|
|
<pre>
|
|
LuaRef v1 (L, 1); // A LUA_TNUMBER
|
|
LuaRef v2 (L, 1.1); // Also a LUA_TNUMBER
|
|
LuaRef v3 (L, true); // A LUA_TBOOLEAN
|
|
LuaRef v4 (L, "string"); // A LUA_TSTRING
|
|
</pre>
|
|
|
|
<p>
|
|
The functions <code>newTable</code> and <code>getGlobal</code> create
|
|
references to new empty table and an existing value in the global table
|
|
respectively:
|
|
</p>
|
|
|
|
<pre>
|
|
LuaRef v1 = newTable (L); // Create a new table
|
|
LuaRef v2 = getGlobal (L, "print") // Reference to _G ["print"]
|
|
</pre>
|
|
|
|
<p>
|
|
A <code>LuaRef</code> can hold classes <em>registered</em> using LuaBridge:
|
|
</p>
|
|
|
|
<pre>
|
|
class A;
|
|
//...
|
|
LuaRef v (L, new A); // A LuaBridge userdata holding a pointer to A
|
|
</pre>
|
|
|
|
<p>
|
|
Any convertible type may be assigned to an already-existing <code>LuaRef</code>:
|
|
</p>
|
|
|
|
<pre>
|
|
LuaRef v (L); // Nil
|
|
v = newTable (L); // An empty table
|
|
v = "string" // A string. The prevous value becomes
|
|
// eligible for garbage collection.
|
|
</pre>
|
|
|
|
<p>
|
|
A <code>LuaRef</code> is itself a convertible type, and the convertible
|
|
type <code>Nil</code> can be used to represent a Lua <strong>nil</strong>.
|
|
</p>
|
|
|
|
<pre>
|
|
LuaRef v1 (L, "x"); // assign "x"
|
|
LuaRef v2 (L, "y"); // assign "y"
|
|
v2 = v1; // v2 becomes "x"
|
|
v1 = "z"; // v1 becomes "z", v2 is unchanged
|
|
v1 = newTable (L); // An empty table
|
|
v2 = v1; // v2 references the same table as v1
|
|
v1 = Nil (); // v1 becomes nil, table is still
|
|
// referenced by v2.
|
|
</pre>
|
|
|
|
<p>
|
|
Values stored in a <code>LuaRef</code> object obey the same rules as
|
|
variables in Lua: tables, functions, threads, and full userdata values are
|
|
<em>objects</em>. The <code>LuaRef</code> does not actually <em>contain</em>
|
|
these values, only <em>references</em> to them. Assignment, parameter
|
|
passing, and function returns always manipulate references to such values;
|
|
these operations do not imply any kind of copy.
|
|
</p>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h3>4.1.1 - <span id="s4.1.1">Type Conversions</span></h3>
|
|
|
|
<p>
|
|
A universal C++ conversion operator is provided for implicit conversions
|
|
which allow a <code>LuaRef</code> to be used where any convertible type is
|
|
expected. These operations will all compile:
|
|
</p>
|
|
|
|
<pre>
|
|
void passInt (int);
|
|
void passBool (bool);
|
|
void passString (std::string);
|
|
void passObject (A*);
|
|
|
|
LuaRef v (L);
|
|
//...
|
|
passInt (v); // implicit conversion to int
|
|
passBool (v); // implicit conversion to bool
|
|
passString (v); // implicit conversion to string
|
|
passObject (v); // must hold a registered LuaBridge class or a
|
|
// lua_error() will be called.
|
|
</pre>
|
|
|
|
<p>
|
|
Since Lua types are dynamic, the conversion is performed at run time using
|
|
traditional functions like <code>lua_toboolean</code> or
|
|
<code>lua_tostring</code>. In some cases, the type information may be
|
|
incorrect especially when passing objects of registered class types.
|
|
When performing these conversions, LuaBridge may raise a Lua error by
|
|
directly or indirectly calling <code>lua_error</code> To be bullet-proof,
|
|
such code must either be wrapped in a <code>lua_pcall</code>, or you must
|
|
install a Lua <em>panic function</em> that throws an exception which you
|
|
can catch.
|
|
</p>
|
|
|
|
<p>
|
|
When an explicit conversion is required (such as when writing templates),
|
|
use the <code>cast</code> template function or an explicit C++ style cast.
|
|
</p>
|
|
|
|
<pre>
|
|
void passString (std::string);
|
|
|
|
LuaRef v (L);
|
|
|
|
// The following are all equivalent:
|
|
|
|
passString (std::string (v));
|
|
passString ((std::string)v);
|
|
passString (static_cast <std::string> (v));
|
|
passString (v.cast <std::string> ());
|
|
</pre>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h3>4.1.2 - <span id="s4.1.2">Visual Studio 2010, 2012</span></h3>
|
|
|
|
<p>
|
|
There is a defect with all versions of Visual Studio up to and including
|
|
Visual Studio 2012 which prevents the implicit conversion operator from
|
|
being applied when it is used as an operand in a boolean operator:
|
|
</p>
|
|
|
|
<pre>
|
|
LuaRef v1 (L);
|
|
LuaRef v2 (L);
|
|
|
|
if (v1 || v2) { } // Compile error in Visual Studio
|
|
|
|
// Work-arounds:
|
|
if (v1.cast <bool> () || v2.cast <bool> ()) { }
|
|
if (bool (v1) || bool (v2)) { }
|
|
</pre>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
</section>
|
|
|
|
<section>
|
|
|
|
<h2>4.2 - <span id="s4.2">Table Proxies</span></h2>
|
|
|
|
<p>
|
|
As tables are the sole data structuring mechanism in Lua, the
|
|
<code>LuaRef</code> class provides robust facilities for accessing and
|
|
manipulating table elements using a simple, precise syntax. Any convertible
|
|
type may be used as a key or value. Applying the array indexing operator
|
|
<code>[]</code> to a <code>LuaRef</code> returns a special temporary object
|
|
called a <em>table proxy</em> which supports all the operations which can
|
|
be performed on a <code>LuaRef</code>. In addition, assignments made to
|
|
table proxies change the underlying table. Because table proxies are
|
|
compiler-created temporary objects, you don't work with them directly. A
|
|
LuaBridge table proxy should not be confused with the Lua proxy table
|
|
technique described in the book "Programming in Lua"; the LuaBridge table
|
|
proxy is simply an intermediate C++ class object that works behind the
|
|
scenes to make table manipulation syntax conform to C++ idioms. These
|
|
operations all invoke table proxies:
|
|
</p>
|
|
|
|
<pre>
|
|
LuaRef v (L);
|
|
v = newTable (L);
|
|
|
|
v ["name"] = "John Doe"; // string key, string value
|
|
v [1] = 200; // integer key, integer value
|
|
v [2] = newTable (L); // integer key, LuaRef value
|
|
v [3] = v [1]; // assign 200 to integer index 3
|
|
v [1] = 100; // v[1] is 100, v[3] is still 200
|
|
v [3] = v [2]; // v[2] and v[3] reference the same table
|
|
v [2] = Nil (); // Removes the value with key = 2. The table
|
|
// is still referenced by v[3].
|
|
</pre>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<section>
|
|
|
|
<h2>4.3 - <span id="s4.3">Calling Lua</span></h2>
|
|
|
|
<p>
|
|
Table proxies and <code>LuaRef</code> objects provide a convenient syntax
|
|
for invoking <code>lua_pcall</code> on suitable referenced object. This
|
|
includes C functions, Lua functions, or Lua objects with an appropriate
|
|
<code>__call</code> metamethod set. The provided implementation supports
|
|
up to eight parameters (although more can be supported by adding new
|
|
functions). Any convertible C++ type can be passed as a parameter in its
|
|
native format. The return value of the function call is provided as a
|
|
<code>LuaRef</code>, which may be <strong>nil</strong>.
|
|
</p>
|
|
|
|
<pre class="split">
|
|
LuaRef same = getGlobal (L, "same");
|
|
|
|
// These all evaluate to true
|
|
same (1,1);
|
|
!same (1,2);
|
|
same ("text", "text");
|
|
!same (1, "text");
|
|
same (1, 1, 2); // third param ignored
|
|
</pre>
|
|
|
|
<pre class="split">
|
|
function same (arg1, arg)
|
|
return arg1 == arg2
|
|
end
|
|
</pre>
|
|
|
|
<p>
|
|
Table proxies support all of the Lua call notation that <code>LuaRef</code>
|
|
supports, making these statements possible:
|
|
</p>
|
|
|
|
<pre class="split">
|
|
LuaRef v = getGlobal (L, "t");
|
|
|
|
t[1]();
|
|
t[2]("a", "b");
|
|
t[2](t[1]); // Call t[3] with the value in t[2]
|
|
t[4]=t[3](); // Call t[3] and store the result in t[4].
|
|
|
|
t [t[5]()] = "wow"; // Store "wow" at the key returned by
|
|
// the call to t[5]
|
|
</pre>
|
|
|
|
<pre class="split">
|
|
t = {}
|
|
t[1] = function () print ("hello") end
|
|
t[2] = function (u, v) print (u, v) end
|
|
t[3] = "foo"
|
|
</pre>
|
|
|
|
<!--========================================================================-->
|
|
|
|
<h3>4.3.1 - <span id="s4.3.1">Class LuaException</span></h3>
|
|
|
|
<section >
|
|
|
|
<p>
|
|
When <code>LuaRef</code> is used to call into Lua using the <code>()</code>
|
|
operator it issues a protected call using <code>lua_pcall</code>. LuaBridge
|
|
uses the C++ exception handling mechanism, throwing a <code>LuaException</code>
|
|
object:
|
|
</p>
|
|
|
|
<pre class="split">
|
|
LuaRef f (L) = getGlobal (L, "fail");
|
|
|
|
try {
|
|
f ();
|
|
}
|
|
catch (LuaException const& e) {
|
|
std::cerr && e.what ();
|
|
}
|
|
</pre>
|
|
|
|
<pre class="split">
|
|
function fail ()
|
|
error ("A problem occurred")
|
|
end
|
|
</pre>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
</section>
|
|
|
|
<section>
|
|
|
|
<h1>5 - <span id="s5">Security</span></h1>
|
|
|
|
<p>
|
|
The metatables and userdata that LuaBridge creates in the `lua_State*` are
|
|
protected using a security system, to eliminate the possibility of undefined
|
|
behavior resulting from scripted manipulation of the environment. The
|
|
security system has these components:
|
|
</p>
|
|
|
|
<ul class="bullets">
|
|
<li>
|
|
Class and const class tables use the <em>table proxy</em> technique. The
|
|
corresponding metatables have <code>__index</code> and <code>__newindex</code>
|
|
metamethods, so these class tables are immutable from Lua.
|
|
<li>
|
|
Metatables have <code>__metatable</code> set to a boolean value. Scripts
|
|
cannot obtain the metatable from a LuaBridge object.
|
|
<li>
|
|
Classes are mapped to metatables through the registry, which Lua scripts
|
|
cannot access. The global environment does not expose metatables
|
|
<li>
|
|
Metatables created by LuaBridge are tagged with a lightuserdata key which
|
|
is unique in the process. Other libraries cannot forge a LuaBridge
|
|
metatable.
|
|
</ul>
|
|
|
|
<p>
|
|
This security system can be easily bypassed if scripts are given access to
|
|
the debug library (or functionality similar to it, i.e. a raw `getmetatable`).
|
|
The security system can also be defeated by C code in the host, either by
|
|
revealing the unique lightuserdata key to another module or by putting a
|
|
LuaBridge metatable in a place that can be accessed by scripts.
|
|
</p>
|
|
|
|
<p>
|
|
When a class member function is called, or class property member accessed,
|
|
the `this` pointer is type-checked. This is because member functions exposed
|
|
to Lua are just plain functions that usually get called with the Lua colon
|
|
notation, which passes the object in question as the first parameter. Lua's
|
|
dynamic typing makes this type-checking mandatory to prevent undefined
|
|
behavior resulting from improper use.
|
|
</p>
|
|
|
|
<p>
|
|
If a type check error occurs, LuaBridge uses the <code>lua_error</code>
|
|
mechanism to trigger a failure. A host program can always recover from
|
|
an error through the use of <code>lua_pcall</code>; proper usage of
|
|
LuaBridge will never result in undefined behavior.
|
|
</p>
|
|
|
|
</section>
|
|
|
|
<!--========================================================================-->
|
|
|
|
</body>
|
|
</html>
|
|
|