Exposing an STL Queue to Lua via Luabind

Question

I'm attempting to replace an existing implementation of a queue class written in Lua with the STL Queue class. I'm not sure why this is failing, or how to approach fixing it. Below is some sample code that exhibits the same behavior, along with the error output. Thanks in advance!

#include <luabind/luabind.hpp>
#include <queue>

struct XYZ_T
{
    short x, y, z;
};

typedef std::queue<XYZ_T> XYZ_QUEUE_T;

extern "C" int init(lua_State *L)
{
    using namespace luabind;

    open(L);

    module(L)
    [
        class_<XZY_T>("XYZ_T")
            .def(constructor<>())
            .def_readwrite("x", &XYZ_T::x)
            .def_readwrite("y", &XYZ_T::y)
            .def_readwrite("z", &XYZ_T::z),

        class_<XYZ_QUEUE_T>("XYZ_QUEUE_T")
            .def(constructor<>())
            .def("push",  &XYZ_QUEUE_T::push)
            .def("pop",   &XYZ_QUEUE_T::pop)
            .def("front", &XYZ_QUEUE_T::front)
            .def("back",  &XYZ_QUEUE_T::back)
            .def("empty", &XYZ_QUEUE_T::empty)
            .def("size",  &XYZ_QUEUE_T::size)
    ];
}

And the gcc output:

g++ -o test_luabind.os -c -fPIC -Iinclude -I$VALID_INCLUDE_DIR /packages/build_env/include test_luabind.cpp
test_luabind.cpp: In function `int init(lua_State*)':
test_luabind.cpp:27: error: no matching function for call to `
   luabind::class_<XYZ_QUEUE_T, luabind::detail::unspecified, 
   luabind::detail::unspecified, luabind::detail::unspecified>::def(const 
   char[6], <unknown type>)'
test_luabind.cpp:32: error: parse error before `(' token

score 4 · Accepted Answer · answered Jul 06 '11 at 23:35

4

Most likely, you have an overloaded function in your queue implementation. Thus, when you take the address, the compiler doesn't know what to do because you could mean any overloaded function.

answered Jul 06 '11 at 23:35

Puppy

144,682
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If this is true, that would be `std::queue::front`, which has a `const` and non-const version. `back` has similar versions. – Nicol Bolas Jul 07 '11 at 02:34
Excellent! That was exactly it. It seems so obvious now :-) – Joe Jul 07 '11 at 14:31

Georg Fritzsche · Answer 2 · 2011-07-07T09:07:57.233

As DeadMG points out, in the case of overloaded functions you have to tell the compiler which version to pick, e.g. for the const versions:

typedef const XYZ_QUEUE_T::value_type& (XYZ_QUEUE_T::*ConstRefConstType)() const;

class_<XYZ_QUEUE_T>("XYZ_QUEUE_T")
    // ...
    .def("front", (ConstRefConstType)&XYZ_QUEUE_T::front)
    .def("back" , (ConstRefConstType)&XYZ_QUEUE_T::back)
    // ...

The luabind documentation includes an example of this.

score 0 · Answer 3 · answered Jul 06 '11 at 22:58

0

This:

class_("XYZ_QUEUE_T")

Should be:

class_<XYZ_QUEUE_T>("XYZ_QUEUE_T")

The string is the typename that Lua sees, while the template parameter is the C++ type you're using.

Oh, and it does little good to expose the queue to Lua if you don't expose the objects that the queue stores.

answered Jul 06 '11 at 22:58

Nicol Bolas

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982

Gah, I had that in there, but I forgot to HTML code the < symbol. Also, defining XYZ_T didn't seem to affect the issue. Long story short, same issue :-( – Joe Jul 06 '11 at 23:05

Exposing an STL Queue to Lua via Luabind

3 Answers3