is_functor_argument_immutable.h

/*  This file is part of the Vc library. {{{
Copyright © 2014-2016 Matthias Kretz <kretz@kde.org>
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#ifndef VC_TRAITS_IS_FUNCTOR_ARGUMENT_IMMUTABLE_H_
#define VC_TRAITS_IS_FUNCTOR_ARGUMENT_IMMUTABLE_H_

namespace Vc_VERSIONED_NAMESPACE
{
namespace Traits
{
namespace is_functor_argument_immutable_impl
{
template <typename F, typename A> std::false_type test(void (F::*)(A &));
template <typename F, typename A> std::false_type test(void (F::*)(A &) const);
template <typename F, typename A> std:: true_type test(void (F::*)(const A &));
template <typename F, typename A> std:: true_type test(void (F::*)(const A &) const);
template <typename F, typename A> std:: true_type test(void (F::*)(const A &&));
template <typename F, typename A> std:: true_type test(void (F::*)(const A &&) const);
template <typename F, typename A> std:: true_type test(void (F::*)(const A));
template <typename F, typename A> std:: true_type test(void (F::*)(const A) const);
template <typename F, typename A> std:: true_type test(void (F::*)(A));
template <typename F, typename A> std:: true_type test(void (F::*)(A) const);

// This function is defined with a forwarding reference. Therefore it can also bind as T
// &, in which case the argument is mutable.
template <typename F, typename A> std::false_type test(void (F::*)(A &&));
template <typename F, typename A> std::false_type test(void (F::*)(A &&) const);

struct dummy {};

// generate a true_type for template operator() members in F that are callable with a
// 'const A &' argument even if the template parameter to operator() is fixed to 'A'.
template <
    typename F, typename A
#ifdef Vc_ICC
    // this ensures that F is a generic lambda. We can be pretty sure that noone wrote a
    // lambda with Vc::Traits::is_functor_argument_immutable_impl::dummy parameter
    // type. In theory, this is not needed because the return type fails with a
    // substitution failure in that case. Only ICC generates and error instead of doing
    // SFINAE.
    ,
    typename = decltype(std::declval<F &>()(std::declval<dummy &>()))
#endif
    ,
    typename MemberPtr = decltype(&F::template operator()<A>)>
decltype(is_functor_argument_immutable_impl::test(std::declval<MemberPtr>())) test2(int);

// generate a true_type for non-template operator() members in F that are callable with a
// 'const A &' argument.
template <typename F, typename A>
decltype(
    is_functor_argument_immutable_impl::test(std::declval<decltype(&F::operator())>()))
test2(float);

template <typename A> std::false_type test3(void (*)(A &));
template <typename A> std:: true_type test3(void (*)(const A &));
template <typename A> std:: true_type test3(void (*)(const A));
template <typename A> std:: true_type test3(void (*)(A));
template <typename A> std:: true_type test3(void (*)(A &&));

}  // namespace is_functor_argument_immutable_impl

template <typename F, typename A, bool = std::is_function<F>::value>
struct is_functor_argument_immutable;
template <typename F, typename A>
struct is_functor_argument_immutable<F, A, false>
    : public decltype(is_functor_argument_immutable_impl::test2<
                      typename std::remove_reference<F>::type, A>(int())) {
};
template <typename F, typename A>
struct is_functor_argument_immutable<F, A, true>
    : public decltype(is_functor_argument_immutable_impl::test3(std::declval<F>())) {
};

}  // namespace Traits
}  // namespace Vc

#endif  // VC_TRAITS_IS_FUNCTOR_ARGUMENT_IMMUTABLE_H_

// vim: foldmethod=marker