callable_traits.h

Go to the documentation of this file.

#ifndef GRPPI_COMMON_CALLABLE_TRAITS_H
#define GRPPI_COMMON_CALLABLE_TRAITS_H

namespace grppi {

namespace internal {

template <typename T>
struct identity {
  using type = T;
};

// Callable helper for function objects defers to pointer to call operator
template <typename T>
struct callable_helper : callable_helper<decltype(&T::operator())>
{};

// Callable helper for function type
template <typename R, typename ... Args>
struct callable_helper<R(Args...)> : identity<R(Args...)>
{
  using arity = typename std::integral_constant<size_t, sizeof...(Args)>::type;
};

// Callable helper for pointer to function defers to callable helper for
// function type
template <typename R, typename ... Args>
struct callable_helper<R(*)(Args...)> : callable_helper<R(Args...)>
{};

// Callalble helper for pointer to const member function defers to callable helper
// for function type
template <typename C, typename R, typename ... Args>
struct callable_helper<R(C::*)(Args...) const> : callable_helper<R(Args...)>
{};

// Callalble helper for pointer to non-const member function defers to callable helper
// for function type
template <typename C, typename R, typename ... Args>
struct callable_helper<R(C::*)(Args...)> : callable_helper<R(Args...)>
{};

// Callable single interface defers to correspondign callable helper
template <typename T>
struct callable : callable_helper<T>
{};

// Convenience meta-function for getting arity of a callable
template <typename T>
constexpr size_t callable_arity() {
  return typename callable<T>::arity();
}

// Meta-function for determining if a callable has arguments
template <typename F>
constexpr bool has_arguments() {
  return typename callable<F>::arity() != 0;
}

} // end namespace internal

// Concept emulation requiring a callable with no arguments
template <typename F>
using requires_no_arguments =
  typename std::enable_if_t<!internal::has_arguments<F>(), int>;

// Concept emulation requiring a callable with one or more arguments
template <typename F>
using requires_arguments =
  typename std::enable_if_t<internal::has_arguments<F>(), int>;




} // end namespace grppi

#endif