objc_msgSend - C++ Lambda

objc_msg_lambda.cpp

#include <functional>
#include <iostream>
#include <objc/runtime.h>
#include <objc/message.h>

template< typename _R_, typename ... _T_ >
_R_ CXX_IMP( id self, SEL _cmd, _T_ ... args )
{
    Class                             cls;
    id                                assoc;
    std::function< _R_( _T_ ... ) > * f;
    
    std::cout << "CXX_IMP: " << self << std::endl;
    
    cls = object_getClass( self );
    
    if( cls == nullptr )
    {
        return;
    }
    
    assoc = objc_getAssociatedObject( reinterpret_cast< id >( cls ), _cmd );
    
    if( assoc == nullptr )
    {
        return;
    }
    
    f = reinterpret_cast< std::function< _R_( _T_ ... ) > * >( assoc );
    
    ( *( f ) )( std::forward< _T_ >( args )... );
}

int main( void )
{
    Class cls;
    
    cls = objc_allocateClassPair( objc_getClass( "NSObject" ), "Foo", 0 );
    
    if( cls == nullptr )
    {
        return EXIT_FAILURE;
    }
    
    if( class_addMethod( cls, sel_registerName( "test" ), reinterpret_cast< IMP >( CXX_IMP< void, int > ), "" ) == false )
    {
        return EXIT_FAILURE;
    }
    
    objc_setAssociatedObject
    (
        reinterpret_cast< id >( cls ),
        sel_registerName( "test" ),
        reinterpret_cast< id >
        (
            new std::function< void( int ) >
            (
                []( int x )
                {
                    std::cout << x << std::endl;
                }
            )
        ),
        OBJC_ASSOCIATION_ASSIGN
    );
    
    objc_registerClassPair( cls );
    
    {
        id o;
        
        o = objc_msgSend( reinterpret_cast< id >( cls ), sel_registerName( "alloc" ) );
        o = objc_msgSend( o, sel_registerName( "init" ) );
        
        objc_msgSend( o, sel_registerName( "test" ), 42 );
        objc_msgSend( o, sel_registerName( "release" ) );
    }
    
    return EXIT_SUCCESS;
}