Question

I remember that when using Boost.Spirit and for the std::function addition to C++0x, you specify the function type by using a syntax that doesn’t use pointers, like in defining std::function<bool(int)> fn, whereas you would cast a pointer like (bool(*)(int))fn.

Can anyone tell me the name of this new syntax or any references on this, or how to use it? It seems like a polymorphic function type syntax that applies for functors as well, but I don’t really know how to use it.

Answer 1

bool(int) is the type of the function; bool(*)(int) is the type of the function pointer. In other words, if you define

typedef bool(BF)(int);
typedef bool(pBF*)(int);

then BF* is the same as pBF.

The std::function template captures the return and argument types via (variadic) templates:

template <typename R, typename ...Args> struct function
{
  function(R(&f)(Args...)); // conceptually
}