Question

Is there any problem with such closure implementation (stolen from python hack)?

void function(int value) {
    struct closure {
        closure(int v = value) : value_(value) {}
        private: int value_;
    };
    closure c;
}

Upon further investigation, it appears in member functions, local variables can not be used as default values, but object variables can.

Answer 1

That looks like a good basis to make a closure. More of an idiom than a hack, since you’re legitimately using language features for their intended purpose.

Of course, your example doesn’t do anything. And it can only be used within function.

Gratuitous C++0x plug:

#include <functional>

void some_function( int x ) { }

void function( int value ) {
    struct closure {
         std::function< void() > operator()( int value )
             { return [=](){ some_function( value ); }; }
    };

    auto a = closure()( value );
    auto b = closure()( 5 );

    a();
    b();
    b();
}