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    <p>The <code>bar</code> functions can be imported into Lua using tolua++ and wrapped to yield an object-style interface, garbage collection included.</p> <p>To demonstrate the passing of arguments, I have changed the <code>bar</code> interface to</p> <pre><code>bar * bar_create(int x); int bar_do_something(bar * baz, int y); void bar_free(bar * baz); </code></pre> <p>and written a test implementation that prints out <code>x</code>, <code>y</code>, etc. when the functions are called.</p> <p>The <code>bar_create()</code> Lua function returns a userdata value. Lua deallocates such user data by calling the <code>__gc</code> method stored in the metatable of the data. Given a <code>userdata</code> value and a destructor <code>gc</code>, the <code>__gc</code> method is overwritten such that it first calls <code>gc</code> and then calls the original <code>gc</code> method:</p> <pre><code>function wrap_garbage_collector(userdata, gc) local mt = getmetatable(userdata) local old_gc = mt.__gc function mt.__gc (data) gc(data) old_gc(data) end end </code></pre> <p>Userdata of the same type share the same metatable; therefore the <code>wrap_garbage_collector()</code> function should be called only once for each class (assuming that tolua++'s metatables are constructed once and deallocated only at exit).</p> <p>At the bottom of this answer is a complete <code>bar.pkg</code> file that imports the <code>bar</code> functions and adds a <code>bar</code> class to a Lua module named <code>foo</code>. The <code>foo</code> module is loaded into the interpreter (<a href="https://stackoverflow.com/questions/4482518/setting-up-an-environment-for-an-embedded-lua-script/4486058#4486058">see for example my SO tolua++ example</a>) and used like this:</p> <pre><code>bars = {} for i = 1, 3 do bars[i] = foo.bar(i) end for i = 1, 3 do local result = bars[i]:do_something(i * i) print("result:", result) end </code></pre> <p>The test implementation prints out what happens:</p> <pre><code>bar(1) bar(2) bar(3) bar(1)::do_something(1) result: 1 bar(2)::do_something(4) result: 8 bar(3)::do_something(9) result: 27 ~bar(3) ~bar(2) ~bar(1) </code></pre> <p>The construction of the <code>bar</code> class below is a little elaborate: the <code>build_class()</code> utility returns a class (a Lua table) given the constructor, destructor, and the class methods. Adjustments will no doubt be needed, but as a prototype demonstration the example should be OK.</p> <pre><code>$#include "bar.hpp" // The bar class functions. bar * bar_create(int x); int bar_do_something(bar * baz, int y); void bar_free(bar * baz); $[ -- Wrapping of the garbage collector of a user data value. function wrap_garbage_collector(userdata, gc) local mt = getmetatable(userdata) local old_gc = mt.__gc function mt.__gc (data) gc(data) old_gc(data) end end -- Construction of a class. -- -- Arguments: -- -- cons : constructor of the user data -- gc : destructor of the user data -- methods : a table of pairs { method = method_fun } -- -- Every 'method_fun' of 'methods' is passed the user data -- as the first argument. -- function build_class(cons, gc, methods) local is_wrapped = false function class (args) -- Call the constructor. local value = cons(args) -- Adjust the garbage collector of the class (once only). if not is_wrapped then wrap_garbage_collector(value, gc) is_wrapped = true end -- Return a table with the methods added. local t = {} for name, method in pairs(methods) do t[name] = function (self, ...) -- Pass data and arguments to the method. return (method(value, ...)) end end return t end return class end -- The Lua module that contains our classes. foo = foo or {} -- Build and assign the classes. foo.bar = build_class(bar_create, bar_free, { do_something = bar_do_something }) -- Clear global functions that shouldn't be visible. bar_create = nil bar_free = nil bar_do_something = nil $] </code></pre>
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    1. PObinding structs and ctor/dtor with tolua++
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    1. COThat is a lot more Lua than I thought I'd have to write, but it looks like it will work as a solution. Thank you very much for your lengthy and well-written answer, I will try this as soon as I'm off work tomorrow.
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    2. COThanks a lot, this was a great answer. My initial hope had been that I didn't have to write the build_class function, since tolua++ already does this for C++ classes, and that somehow I could do this purely with tolua++ syntax in the pkg file and no embedded lua code. Also, your solution exports the bar_create and bar_free symbols, which the user of the module shouldn't use explicitly, so that's not so pretty. But it's a solution, and I'll go with this for my library, so here's the bounty!
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    3. CO@Enno The example stores local references to the functions, so its OK overwrite the global variables at the end. I've added this to the example.
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