116 lines
4.3 KiB
C++
116 lines
4.3 KiB
C++
// Copyright 2020 The Tint Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef SRC_TRAITS_H_
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#define SRC_TRAITS_H_
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#include <tuple>
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namespace tint {
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namespace traits {
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/// Convience type definition for std::decay<T>::type
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template <typename T>
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using Decay = typename std::decay<T>::type;
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/// NthTypeOf returns the `N`th type in `Types`
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template <int N, typename... Types>
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using NthTypeOf = typename std::tuple_element<N, std::tuple<Types...>>::type;
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/// Signature describes the signature of a function.
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template <typename RETURN, typename... PARAMETERS>
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struct Signature {
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/// The return type of the function signature
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using ret = RETURN;
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/// The parameters of the function signature held in a std::tuple
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using parameters = std::tuple<PARAMETERS...>;
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/// The type of the Nth parameter of function signature
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template <std::size_t N>
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using parameter = NthTypeOf<N, PARAMETERS...>;
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/// The total number of parameters
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static constexpr std::size_t parameter_count = sizeof...(PARAMETERS);
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};
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/// SignatureOf is a traits helper that infers the signature of the function,
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/// method, static method, lambda, or function-like object `F`.
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template <typename F>
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struct SignatureOf {
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/// The signature of the function-like object `F`
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using type = typename SignatureOf<decltype(&F::operator())>::type;
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};
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/// SignatureOf specialization for a regular function or static method.
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template <typename R, typename... ARGS>
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struct SignatureOf<R (*)(ARGS...)> {
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/// The signature of the function-like object `F`
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using type = Signature<typename std::decay<R>::type,
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typename std::decay<ARGS>::type...>;
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};
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/// SignatureOf specialization for a non-static method.
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template <typename R, typename C, typename... ARGS>
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struct SignatureOf<R (C::*)(ARGS...)> {
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/// The signature of the function-like object `F`
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using type = Signature<typename std::decay<R>::type,
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typename std::decay<ARGS>::type...>;
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};
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/// SignatureOf specialization for a non-static, const method.
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template <typename R, typename C, typename... ARGS>
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struct SignatureOf<R (C::*)(ARGS...) const> {
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/// The signature of the function-like object `F`
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using type = Signature<typename std::decay<R>::type,
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typename std::decay<ARGS>::type...>;
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};
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/// SignatureOfT is an alias to `typename SignatureOf<F>::type`.
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template <typename F>
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using SignatureOfT = typename SignatureOf<F>::type;
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/// ParameterType is an alias to `typename SignatureOf<F>::type::parameter<N>`.
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template <typename F, std::size_t N>
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using ParameterType = typename SignatureOfT<F>::template parameter<N>;
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/// ReturnType is an alias to `typename SignatureOf<F>::type::ret`.
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template <typename F>
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using ReturnType = typename SignatureOfT<F>::ret;
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/// `IsTypeOrDerived<T, BASE>::value` is true iff `T` is of type `BASE`, or
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/// derives from `BASE`.
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template <typename T, typename BASE>
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using IsTypeOrDerived =
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std::integral_constant<bool,
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std::is_base_of<BASE, Decay<T>>::value ||
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std::is_same<BASE, Decay<T>>::value>;
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/// If `CONDITION` is true then EnableIf resolves to type T, otherwise an
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/// invalid type.
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template <bool CONDITION, typename T>
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using EnableIf = typename std::enable_if<CONDITION, T>::type;
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/// If `T` is of type `BASE`, or derives from `BASE`, then EnableIfIsType
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/// resolves to type `T`, otherwise an invalid type.
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template <typename T, typename BASE>
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using EnableIfIsType = EnableIf<IsTypeOrDerived<T, BASE>::value, T>;
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/// If `T` is not of type `BASE`, or does not derive from `BASE`, then
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/// EnableIfIsNotType resolves to type `T`, otherwise an invalid type.
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template <typename T, typename BASE>
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using EnableIfIsNotType = EnableIf<!IsTypeOrDerived<T, BASE>::value, T>;
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} // namespace traits
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} // namespace tint
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#endif // SRC_TRAITS_H_
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