Re: passing pointers using LuaBridge

[Jeremy Ong <jeremycong@...>]

Out of curiosity, have you tried Selene? You can register classes and
pass pointers to those classes. See the test case at:

https://github.com/jeremyong/Selene/blob/master/test/class_tests.h#L103

The definitions of the Bar and Zoo classes of that test case are at
the top of that file. Aside from those definitions, the code in that
test case is self-contained.

On Mon, Apr 7, 2014 at 1:38 AM, Andrew Starks <andrew.starks@trms.com> wrote:
>
>
> On Monday, April 7, 2014, Moose <moose@posteo.de> wrote:
>>
>> Hi all,
>>
>> I am making moderate progress integrating Lua into my C++ environment.
>> After trying many different ways of wrapping C or C++ code I ended up with
>> two candidates that seemed to suit my needs best. LuaBridge
>> (https://github.com/vinniefalco/LuaBridge) and LuaWrapper
>> (https://bitbucket.org/alexames/luawrapper).
>>
>> I was able to create C++ wrappers for existing classes with both, and,
>> inside my scripts, to create objects of those types and call methods upon
>> them. So far so good. However, with both implementations I have failed to
>> pass existing objects with C++ lifetime into the script.
>>
>> With LuaBridge for example I do this (simplified):
>>
>> int luaopen_mylib_1(lua_State *L) {
>>
>>         using namespace luabridge;
>>         getGlobalNamespace(L)
>>                 .beginNamespace("mylib")
>>                         .addFunction ("testfree", testfree)
>>                         .beginClass<MyClass>("MyClass")
>>                                 .addFunction("foo",   &MyClass::foo   )
>>                         .endClass()
>>                 .endNamespace();
>>
>>         // quite like this interface btw.
>>
>>         return 0;
>> }
>>
>> ... then ...
>>
>>    using namespace luabridge;
>>    lua_State *L = luaL_newstate();
>>    luaL_openlibs(L);
>>
>>    // and register the functions within that context
>>    luaopen_mylib_1(L);
>>
>>    // create MyClass instance
>>    MyClass *p = new MyClass();
>>    setGlobal(L, p, "mc");     // a LuaBridge Method that pushes the
>> pointer as
>>                                          // global userdata on the stack
>>
>>    if (luaL_dofile(L, "luawrapper_reuse.lua")) {
>>                 std::cerr << "Lua program returned an error: \n";
>>                 std::cerr << lua_tostring(L, -1);
>>                 std::cerr << std::endl;
>>                 lua_close(L);
>>    }
>>
>>    delete p;
>>
>>
>>
>> All very straight forward.
>> Then in my script...
>>
>> [[
>> print("Executing LuaBridge test")
>> mylib.testfree()
>> mc:foo()
>> ]]
>>
>> The method testfree() is being called all right. At least I see the
>> output. But then, when I try to access the instance "mc", I get:
>>
>> luawrapper_reuse.lua:6: attempt to index global 'mc' (a userdata value)
>>
>>
>> Despite the fact that I do everything by the book, exactly the way it is
>> described in LuaBridges manual. Can anyone tell me what I do wrong? How can
>> I access the object?
>> It seems like Lua does know it. A pointer by the name 'mc' has been pushed
>> as userdata into the context, which is how I understand this is supposed to
>> work. But why can I not de-reference it and call a method?
>> So close to the goal and yet all my efforts fail on this....
>>
>> With that Test I use LuaJit 2.0 on Windows64 (MSVC9).
>>
>>
>> Help is much appreciated.
>>
>> Thanks,
>> Moose.
>>
>>
>>
>
> Smart guy question: have you tried "Lua the C API?"
>
> But that's an question from someone who only trusts his own abstractions...
> Nothing to see here...