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<!doctype html>
<html>
<head>
<title>LuaBridge 2.0 Reference Manual</title>
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<!--=========================================================================-->
<body>
<header>
<hr>
<h1>LuaBridge 2.0 Reference Manual</h1>
<hr>
</header>
<small>
Official repository is located at
<a href="https://github.com/vinniefalco/LuaBridge">https://github.com/vinniefalco/LuaBridge</a>.
<br>
Copyright © 2012 Vinnie Falco. Freely available under the terms of the
<A HREF="http://www.opensource.org/licenses/mit-license.html">MIT License</A>.
</small>
<nav>
<H2>Contents</H2>
<UL id="toc" style="padding: 0">
<LI><A href="#s1">1 - Introduction</A>
<UL>
<LI><A href="#s1.1">1.1 - Design</A>
<LI><A href="#s1.2">1.2 - Repository</A>
<LI><A href="#s1.3">1.3 - License and Credits</A>
</UL>
<P>
<LI><A href="#s2">2 - Accessing C++ from Lua</A>
<UL>
<LI><A href="#s2.1">2.1 - Namespaces</A>
<LI><A href="#s2.2">2.2 - Data, Properties, Functions, and CFunctions</A>
<LI><A href="#s2.3">2.3 - Class Objects</A>
<LI><A href="#s2.4">2.4 - Property Member Proxies</A>
<LI><A href="#s2.5">2.5 - Constructors</A>
<LI><A href="#s2.6">2.6 - Lua Stack</A>
<LI><A href="#s2.7">2.7 - lua_State</A>
</UL>
<p>
<LI><A href="#s3">3 - Passing Objects</A>
<UL>
<LI><A href="#s3.1">3.1 - C++ Lifetime</A>
<LI><A href="#s3.2">3.2 - Lua Lifetime</A>
<LI><A href="#s3.3">3.3 - Pointers, References, and Pass by Value</A>
<LI><A href="#s3.4">3.4 - Shared Lifetime</A>
<UL>
<LI><A href="#s3.4.1">3.4.1 - Class RefCountedObjectPtr</A>
<LI><A href="#s3.4.2">3.4.2 - Class RefCountedPtr</A>
<LI><A href="#s3.4.3">3.4.3 - User-defined Containers</A>
<LI><A href="#s3.4.4">3.4.4 - Container Constructors</A>
</UL>
<LI><A href="#s3.5">3.5 - Mixing Lifetimes</A>
<LI><A href="#s3.6">3.6 - Convenience Functions</A>
</UL>
<P>
<LI><A href="#s4">4 - Accessing Lua from C++</A>
<UL>
<LI><A href="#s4.1">4.1 - Class LuaRef</A>
<UL>
<LI><A href="#s4.1.1">4.1.1 - Type Conversions</A>
<LI><A href="#s4.1.2">4.1.2 - Visual Studio 2010, 2012</A>
</UL>
<LI><A href="#s4.2">4.2 - Table Proxies</A>
<LI><A href="#s4.3">4.3 - Calling Lua</A>
<UL>
<LI><A href="#s4.3.1">4.3.1 - Class LuaException</A>
</UL>
</uL>
<P>
<LI><A href="#s5">5 - Security</A>
</UL>
</nav>
<!--========================================================================-->
<section>
<h1>1 - <span id="s1">Introduction</span></h1>
<p>
<a href="https://github.com/vinniefalco/LuaBridge">LuaBridge</a> is a
lightweight and dependency-free library for mapping data, functions, and
classes back and forth between C++ and <a href="http://wwww.lua.org">Lua</a>,
a powerful, fast, lightweight, embeddable scripting language. LuaBridge has
been tested and works with Lua revisions starting from 5.1.5, although it
should work in any version of Lua from 5.1.0 and later. It also works
transparently with <a href="http://luajit.org/">LuaJIT</a>.
</p>
<p>
LuaBridge offers the following features:
</p>
<ul class="bullets" title="Features">
<li><a href="http://www.opensource.org/licenses/mit-license.html">MIT Licensed</a>, no usage restrictions!</li>
<li>Headers-only: No Makefile, no .cpp files, just one <code>#include</code>!</li>
<li>Simple, light, and nothing else needed (like Boost).</li>
<li>No macros, settings, or configuration scripts needed.</li>
<li>Supports different object lifetime management models.</li>
<li>Convenient, type-safe access to the Lua stack.</li>
<li>Automatic function parameter type binding.</li>
<li>Easy access to Lua objects like tables and functions.</li>
<li>Written in a clear and easy to debug style.</li>
<li>Does not require C++11.</li>
</ul>
<p>
LuaBridge is distributed as a a collection of header files. You simply add
one line, <code>#include "LuaBridge/LuaBridge.h"</code> where you want to
pass functions, classes, and variables back and forth between C++ and Lua.
There are no additional source files, no compilation settings, and no
Makefiles or IDE-specific project files. LuaBridge is easy to integrate.
</p>
<p>
C++ concepts like variables and classes are made available to Lua through a
process called <em>registration</em>. Because Lua is weakly typed, the resulting
structure is not rigid. The API is based on C++ template metaprogramming. It
contains template code to automatically generate at compile-time the various
Lua C API calls necessary to export your program's classes and functions to
the Lua environment.
</p>
<p>
To expose Lua objects to C++, a class called <code>LuaRef</code> is provided.
The implementation allows C++ code to access Lua objects such as numbers
or strings, but more importantly to access things like tables and their
values. Using this class makes idioms like calling Lua functions simple
and clean.
</p>
<!--========================================================================-->
<section>
<h2>1.1 - <span id="s1.1">Design</span></h2>
<p>
LuaBridge tries to be efficient as possible when creating the "glue" that
exposes C++ data and functions to Lua. At the same time, the code was
written with the intention that it is all as simple and clear as possible,
without resorting to obscure C++ idioms, ugly preprocessor macros, or
configuration settings. Furthermore, it is designed to be "header-only",
making it very easy to integrate into your projects.
</p>
<p>
Because LuaBridge was written with simplicity in mind there are some features
that are not available. Although it comes close to the highest possible
performance, LuaBridge is not quite the fastest,
<a href="http://code.google.com/p/oolua/">OOLua</a> slightly outperforms
LuaBridge in some tests. LuaBridge also does not try to implement every
possible feature,
<a href="http://www.rasterbar.com/products/luabind.html">LuaBind</a>
explores every corner of the C++ language (but it requires Boost).
</p>
<p>
LuaBridge does not support:
</p>
<ul class="bullets">
<li>Enumerated constants
<li>More than 8 parameters on a function or method (although this can be
increased by adding more <code>TypeListValues</code> specializations).
<li>Overloaded functions, methods, or constructors.
<li>Global variables (variables must be wrapped in a named scope).
<li>Automatic conversion between STL container types and Lua tables.
<li>Inheriting Lua classes from C++ classes.
<li>Passing nil to a C++ function that expects a pointer or reference.
<li>Standard containers like <code>std::shared_ptr</code>.
</ul>
</section>
<!--========================================================================-->
<section>
<h2>1.2 - <span id="s1.2">Repository</span></h2>
<p>
The official repository is located at
<a href="https://github.com/vinniefalco/LuaBridge">https://github.com/vinniefalco/LuaBridge</a>.
The branches are organized as follows:
</p>
<table>
<tr>
<td><b>master</b></td>
<td>Tagged, stable release versions.</td>
</tr>
<tr>
<td><b>release</b></td>
<td>A temporarily created branch that holds a release candidate for review.</td>
</tr>
<tr>
<td><b>develop</b></td>
<td>Contains work in progress, possibly unfinished or with bugs.</td>
</tr>
</table>
<p>
These repositories are also available:
</p>
<table>
<tr>
<td><b><a href="https://github.com/vinniefalco/LuaBridgeUnitTests">LuaBridgeUnitTests</a></b></td>
<td>A stand alone command line application to exercise LuaBridge functionality.</td>
</tr>
<tr>
<td><b><a href="https://github.com/vinniefalco/LuaBridgeDemo">LuaBridgeUnitDemo</a></b></td>
<td>A stand alone GUI application that provides an interactive console.</td>
</tr>
</table>
</section>
<!--========================================================================-->
<section>
<h2>1.3 - <span id="s1.3">License and Credits</span></h2>
<p>
LuaBridge is published under the terms of the
<a href="http://www.opensource.org/licenses/mit-license.html">MIT License</a>:
</p>
<pre>
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
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
</pre>
<p>
The original version of LuaBridge was written by Nathan Reed. The project
has been taken over by Vinnie Falco, who added new functionality and wrote
the new documentation. Vinnie also incorporated <code>LuaRef</code> and
other Lua to C++ binding contributions from Nigel Atkinson.
</p>
<p>
For questions, comments, or bug reports feel free to open a Github issue
or contact Vinnie Falco directly at the email address indicated below.
</p>
<ul>
<li>Copyright 2012, Vinnie Falco <a href="mailto:vinnie.falco@gmail.com"><vinnie.falco@gmail.com></a>
<li>Copyright 2008, Nigel Atkinson <a href="mailto:suprapilot+LuaCode@gmail.com"><suprapilot+LuaCode@gmail.com></a>
<li>Copyright 2007, Nathan Reed
<li>Portions from The Loki Library: Copyright 2001 by Andrei Alexandrescu
</ul>
<p>
Older versions of LuaBridge up to and including 0.2 (available separately) are
distributed under the BSD 3-Clause License. See the corresponding license file
in those versions (distributed separately) for more details.
</p>
</section>
<!--========================================================================-->
</section>
<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
information must be <em>registered</em>. There are five types of objects that
LuaBridge can register:
</p>
<table>
<tr>
<td><b>Namespaces</b> </td>
<td>A Lua table that contains other registrations.</td>
</tr>
<tr>
<td><b>Data</b> </td>
<td>Global or static variables, data members, and static data members.</td>
</tr>
<tr>
<td><b>Functions </b></td>
<td>Regular functions, member functions, and static member functions.</td>
</tr>
<tr>
<td><b>CFunctions </b></td>
<td>A regular function, member function, or static member function that
uses the <code>lua_CFunction</code> calling convention.</td>
</tr>
<tr>
<td><b>Properties </b></td>
<td>Global properties, property members, and static property members.
These appear like data to Lua, but are implemented in C++ using
functions to get and set the values.</td>
</tr>
</table>
<p>
Both data and properties can be marked as <em>read-only</em> at the time of
registration. This is different from <code>const</code>; the values of these
objects can be modified on the C++ side, but Lua scripts cannot change them.
Code samples that follow are in C++ or Lua, depending on context. For brevity
of exposition code samples in C++ assume the traditional variable
<code>lua_State* L</code> is defined, and that a <code>using namespace luabridge</code>
using-directive is in effect.
</p>
<!--========================================================================-->
<section>
<h2>2.1 - <span id="s2.1">Namespaces</span></h2>
<p>
All LuaBridge registrations take place in a <em>namespace</em>. When we refer
to a <em>namespace</em> we are always talking about a namespace in the Lua
sense, which is implemented using tables. The namespace need not correspond
to a C++ namespace; in fact no C++ namespaces need to exist at all unless you
want them to. LuaBridge namespaces are visible only to Lua scripts; they are
used as a logical grouping tool. To obtain access to the global namespace
we write:
</p>
<pre>
getGlobalNamespace (L);
</pre>
<p>
This returns an object on which further registrations can be performed. The
subsequent registrations will go into the global namespace, a practice which
is not recommended. Instead, we can add our own namespace by writing:
</p>
<pre>
getGlobalNamespace (L)
.beginNamespace ("test");
</pre>
<p>
This creates a table in <code>_G</code> called "test". Since we have not
performed any registrations, this table will be empty except for some
bookkeeping key/value pairs. LuaBridge reserves all identifiers that start
with a double underscore. So <code>__test</code> would be an invalid name
(although LuaBridge will silently accept it). Functions like
<code>beginNamespace</code> return the corresponding object on which we can
make more registrations. Given:
</p>
<pre>
getGlobalNamespace (L)
.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>