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/*
* Copyright 2022 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#pragma once
#include <ftl/details/mixins.h>
namespace android::ftl {
// CRTP mixins for defining type-safe wrappers that are distinct from their underlying type. Common
// uses are IDs, opaque handles, and physical quantities. The constructor is provided by (and must
// be inherited from) the `Constructible` mixin, whereas operators (equality, ordering, arithmetic,
// etc.) are enabled through inheritance:
//
// struct Id : ftl::Constructible<Id, std::int32_t>, ftl::Equatable<Id> {
// using Constructible::Constructible;
// };
//
// static_assert(!std::is_default_constructible_v<Id>);
//
// Unlike `Constructible`, `DefaultConstructible` allows default construction. The default value is
// zero-initialized unless specified:
//
// struct Color : ftl::DefaultConstructible<Color, std::uint8_t>,
// ftl::Equatable<Color>,
// ftl::Orderable<Color> {
// using DefaultConstructible::DefaultConstructible;
// };
//
// static_assert(Color() == Color(0u));
// static_assert(ftl::to_underlying(Color(-1)) == 255u);
// static_assert(Color(1u) < Color(2u));
//
// struct Sequence : ftl::DefaultConstructible<Sequence, std::int8_t, -1>,
// ftl::Equatable<Sequence>,
// ftl::Orderable<Sequence>,
// ftl::Incrementable<Sequence> {
// using DefaultConstructible::DefaultConstructible;
// };
//
// static_assert(Sequence() == Sequence(-1));
//
// The underlying type need not be a fundamental type:
//
// struct Timeout : ftl::DefaultConstructible<Timeout, std::chrono::seconds, 10>,
// ftl::Equatable<Timeout>,
// ftl::Addable<Timeout> {
// using DefaultConstructible::DefaultConstructible;
// };
//
// using namespace std::chrono_literals;
// static_assert(Timeout() + Timeout(5s) == Timeout(15s));
//
template <typename Self, typename T>
struct Constructible {
explicit constexpr Constructible(T value) : value_(value) {}
explicit constexpr operator const T&() const { return value_; }
private:
template <typename, template <typename> class>
friend class details::Mixin;
T value_;
};
template <typename Self, typename T, auto kDefault = T{}>
struct DefaultConstructible : Constructible<Self, T> {
using Constructible<Self, T>::Constructible;
constexpr DefaultConstructible() : DefaultConstructible(T{kDefault}) {}
};
// Shorthand for casting a type-safe wrapper to its underlying value.
template <typename Self, typename T>
constexpr const T& to_underlying(const Constructible<Self, T>& c) {
return static_cast<const T&>(c);
}
// Comparison operators for equality.
template <typename Self>
struct Equatable : details::Mixin<Self, Equatable> {
constexpr bool operator==(const Self& other) const {
return to_underlying(this->self()) == to_underlying(other);
}
constexpr bool operator!=(const Self& other) const { return !(*this == other); }
};
// Comparison operators for ordering.
template <typename Self>
struct Orderable : details::Mixin<Self, Orderable> {
constexpr bool operator<(const Self& other) const {
return to_underlying(this->self()) < to_underlying(other);
}
constexpr bool operator>(const Self& other) const { return other < this->self(); }
constexpr bool operator>=(const Self& other) const { return !(*this < other); }
constexpr bool operator<=(const Self& other) const { return !(*this > other); }
};
// Pre-increment and post-increment operators.
template <typename Self>
struct Incrementable : details::Mixin<Self, Incrementable> {
constexpr Self& operator++() {
++this->mut();
return this->self();
}
constexpr Self operator++(int) {
const Self tmp = this->self();
operator++();
return tmp;
}
};
// Additive operators, including incrementing.
template <typename Self>
struct Addable : details::Mixin<Self, Addable>, Incrementable<Self> {
constexpr Self& operator+=(const Self& other) {
this->mut() += to_underlying(other);
return this->self();
}
constexpr Self operator+(const Self& other) const {
Self tmp = this->self();
return tmp += other;
}
private:
using Base = details::Mixin<Self, Addable>;
using Base::mut;
using Base::self;
};
} // namespace android::ftl
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