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160 lines
6.3 KiB
160 lines
6.3 KiB
// Copyright 2021 Google LLC
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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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// https://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 dap_traits_h
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#define dap_traits_h
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#include <tuple>
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#include <type_traits>
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namespace dap {
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namespace traits {
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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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// `IsTypeOrDerived<BASE, T>::value` is true iff `T` is of type `BASE`, or
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// derives from `BASE`.
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template <typename BASE, typename T>
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using IsTypeOrDerived = std::integral_constant<
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bool,
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std::is_base_of<BASE, typename std::decay<T>::type>::value ||
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std::is_same<BASE, typename std::decay<T>::type>::value>;
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// `EachIsTypeOrDerived<N, BASES, TYPES>::value` is true iff all of the types in
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// the std::tuple `TYPES` is of, or derives from the corresponding indexed type
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// in the std::tuple `BASES`.
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// `N` must be equal to the number of types in both the std::tuple `BASES` and
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// `TYPES`.
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template <int N, typename BASES, typename TYPES>
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struct EachIsTypeOrDerived {
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using base = typename std::tuple_element<N - 1, BASES>::type;
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using type = typename std::tuple_element<N - 1, TYPES>::type;
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using last_matches = IsTypeOrDerived<base, type>;
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using others_match = EachIsTypeOrDerived<N - 1, BASES, TYPES>;
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static constexpr bool value = last_matches::value && others_match::value;
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};
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// EachIsTypeOrDerived specialization for N = 1
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template <typename BASES, typename TYPES>
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struct EachIsTypeOrDerived<1, BASES, TYPES> {
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using base = typename std::tuple_element<0, BASES>::type;
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using type = typename std::tuple_element<0, TYPES>::type;
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static constexpr bool value = IsTypeOrDerived<base, type>::value;
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};
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// EachIsTypeOrDerived specialization for N = 0
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template <typename BASES, typename TYPES>
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struct EachIsTypeOrDerived<0, BASES, TYPES> {
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static constexpr bool value = true;
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};
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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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// `HasSignature<F, S>::value` is true iff the function-like `F` has a matching
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// signature to the function-like `S`.
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template <typename F, typename S>
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using HasSignature = std::integral_constant<
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bool,
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std::is_same<SignatureOfT<F>, SignatureOfT<S>>::value>;
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// `Min<A, B>::value` resolves to the smaller value of A and B.
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template <std::size_t A, std::size_t B>
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using Min = std::integral_constant<std::size_t, (A < B ? A : B)>;
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// `CompatibleWith<F, S>::value` is true iff the function-like `F`
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// can be called with the argument types of the function-like `S`. Return type
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// of the two functions are not considered.
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template <typename F, typename S>
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using CompatibleWith = std::integral_constant<
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bool,
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(SignatureOfT<S>::parameter_count == SignatureOfT<F>::parameter_count) &&
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EachIsTypeOrDerived<Min<SignatureOfT<S>::parameter_count,
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SignatureOfT<F>::parameter_count>::value,
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typename SignatureOfT<S>::parameters,
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typename SignatureOfT<F>::parameters>::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 = void>
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using EnableIf = typename std::enable_if<CONDITION, T>::type;
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// If `BASE` is a base of `T` then EnableIfIsType resolves to type `TRUE_TY`,
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// otherwise an invalid type.
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template <typename BASE, typename T, typename TRUE_TY = void>
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using EnableIfIsType = EnableIf<IsTypeOrDerived<BASE, T>::value, TRUE_TY>;
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// If the function-like `F` has a matching signature to the function-like `S`
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// then EnableIfHasSignature resolves to type `TRUE_TY`, otherwise an invalid type.
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template <typename F, typename S, typename TRUE_TY = void>
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using EnableIfHasSignature = EnableIf<HasSignature<F, S>::value, TRUE_TY>;
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} // namespace traits
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} // namespace dap
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#endif // dap_traits_h
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