Cannot inititialize std::function implicitly

Question

I\'ve written this functor to perform an and operation (&&):

// unary functor; performs \'&&\'
template 
         


        

Answer 1

I suggest not abusing std::function and taking normal generic parameters instead. Treat std::function as a type-erased container for callable objects of a particular signature (see https://stackoverflow.com/a/11629125/46642 for more details).

// unary functor; performs '&&'
template 
struct AND
{
    X x;
    Y y;

    template 
    AND(XX&& xx, YY&& yy) 
             : x(std::forward(xx)), y(std::forward(yy)) {}

    template 
    auto operator() ( const T &arg ) -> decltype(x(arg) && y(arg))
    { return x(arg) && y(arg); }
};

template 
using Decay = typename std::decay::type;

// helper
template 
AND, Decay> And(X&& xx, Y&& yy)
{
    return AND, Decay>(std::forward(xx), std::forward(yy));
}