How can I make the storage of C++ lambda objects more efficient?

Question

I\'ve been thinking about storing C++ lambda\'s lately. The standard advice you see on the Internet is to store the lambda in a std::function object. However, none of this adv

Answer 1

The problem is that std::function doesn't use move semantics and copies the lambda around while initializating. It's a bad implementation by MS.

Here is a little trick you can use to get around the problem.

template
class move_lambda
{
    T func_;

public:
    move_lambda(T&& func) : func_(std::move(func)){}            
    move_lambda(const move_lambda& other) : func_(std::move(other.func_)){} // move on copy 
    auto operator()() -> decltype(static_cast(0)()){return func_();}
};

template 
move_lambda make_move_lambda(T&& func)
{
    return move_lambda(std::move(func));
}

usage:

int main()
{
    Simple test( 5 );

    std::function f(make_move_lambda(
        [test] ()
        {
            return test.Get();
        }));

    printf( "%d\n", f() );
}