mfbt/FunctionTypeTraits.h
author L10n Bumper Bot <release+l10nbumper@mozilla.com>
Thu, 08 Nov 2018 03:00:11 -0800
changeset 501100 1cd4f2d571554c4dc89cf1be1d98683c0d14f797
parent 489390 85f7b7200eea172cc5cc1d4eb853cb5062a35baa
child 508163 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
no bug - Bumping Fennec l10n changesets r=release a=l10n-bump DONTBUILD an -> 336e061995b9 ar -> f6834a7d7374 as -> d2c76e616a66 ast -> fcb8f3455237 az -> c4caf3b07cf2 be -> 697eb1022498 bg -> 7bf1f448f743 bn-BD -> 5f7a87adee06 bn-IN -> 49ce3195c4c2 br -> 41cf35b7c5b5 bs -> 4a14aee27904 ca -> 9373e8ce86d4 cak -> a40d767541ba cs -> 4b99defb0525 cy -> 4c948fed2584 de -> 017a7e7a267a dsb -> aadebeccf5ba el -> 2d28a78dcef5 en-CA -> 55ad9171a9f0 en-GB -> 296422b495e9 en-ZA -> c1b5d2128914 eo -> c68e87667d9f es-AR -> bff0a788c711 es-CL -> 1d3efd2532ea es-ES -> 4d1feb70b0e2 es-MX -> fceda607d0f4 et -> 58a8262a0cc7 eu -> 7cebfd46208b fa -> cbc040d58476 ff -> 46f5aec275ea fi -> 235ab13d261e fr -> 8ee417b64f99

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* Helpers to manipulate function types that don't fit in TypeTraits.h */

#ifndef mozilla_FunctionTypeTraits_h
#define mozilla_FunctionTypeTraits_h

#include <tuple>

namespace mozilla {

// Main FunctionTypeTraits declaration, taking one template argument.
//
// Given a function type, FunctionTypeTraits will expose the following members:
// - ReturnType: Return type.
// - arity: Number of parameters (size_t).
// - ParameterType<N>: Type of the Nth** parameter, 0-indexed.
//
// ** `ParameterType<N>` with `N` >= `arity` is allowed and gives `void`.
// This prevents compilation errors when trying to access a type outside of the
// function's parameters, which is useful for parameters checks, e.g.:
//   template<typename F>
//   auto foo(F&&)
//    -> enable_if(FunctionTypeTraits<F>::arity == 1 &&
//                 is_same<FunctionTypeTraits<F>::template ParameterType<0>,
//                         int>::value,
//                 void)
//   {
//     // This function will only be enabled if `F` takes one `int`.
//     // Without the permissive ParameterType<any N>, it wouldn't even compile.
//
// Note: FunctionTypeTraits does not work with generic lambdas `[](auto&) {}`,
// because parameter types cannot be known until an actual invocation when types
// are inferred from the given arguments.
template<typename T>
struct FunctionTypeTraits;

// Remove reference and pointer wrappers, if any.
template<typename T>
struct FunctionTypeTraits<T&> : public FunctionTypeTraits<T>
{
};
template<typename T>
struct FunctionTypeTraits<T&&> : public FunctionTypeTraits<T>
{
};
template<typename T>
struct FunctionTypeTraits<T*> : public FunctionTypeTraits<T>
{
};

// Extract `operator()` function from callables (e.g. lambdas, std::function).
template<typename T>
struct FunctionTypeTraits : public FunctionTypeTraits<decltype(&T::operator())>
{
};

namespace detail {

// If `safe`, retrieve the `N`th type from `As`, otherwise `void`.
// See top description for reason.
template<bool safe, size_t N, typename... As>
struct TupleElementSafe;
template<size_t N, typename... As>
struct TupleElementSafe<true, N, As...>
{
  using Type = typename std::tuple_element<N, std::tuple<As...>>::type;
};
template<size_t N, typename... As>
struct TupleElementSafe<false, N, As...>
{
  using Type = void;
};

template<typename R, typename... As>
struct FunctionTypeTraitsHelper
{
  using ReturnType = R;
  static constexpr size_t arity = sizeof...(As);
  template<size_t N>
  using ParameterType =
    typename TupleElementSafe<(N < sizeof...(As)), N, As...>::Type;
};

} // namespace detail

// Specialization for free functions.
template<typename R, typename... As>
struct FunctionTypeTraits<R(As...)> : detail::FunctionTypeTraitsHelper<R, As...>
{
};

// Specialization for non-const member functions.
template<typename C, typename R, typename... As>
struct FunctionTypeTraits<R (C::*)(As...)>
  : detail::FunctionTypeTraitsHelper<R, As...>
{
};

// Specialization for const member functions.
template<typename C, typename R, typename... As>
struct FunctionTypeTraits<R (C::*)(As...) const>
  : detail::FunctionTypeTraitsHelper<R, As...>
{
};

#ifdef NS_HAVE_STDCALL
// Specialization for __stdcall free functions.
template<typename R, typename... As>
struct FunctionTypeTraits<R NS_STDCALL(As...)>
  : detail::FunctionTypeTraitsHelper<R, As...>
{
};

// Specialization for __stdcall non-const member functions.
template<typename C, typename R, typename... As>
struct FunctionTypeTraits<R (NS_STDCALL C::*)(As...)>
  : detail::FunctionTypeTraitsHelper<R, As...>
{
};

// Specialization for __stdcall const member functions.
template<typename C, typename R, typename... As>
struct FunctionTypeTraits<R (NS_STDCALL C::*)(As...) const>
  : detail::FunctionTypeTraitsHelper<R, As...>
{
};
#endif // NS_HAVE_STDCALL

} // namespace mozilla

#endif // mozilla_FunctionTypeTraits_h