| // Copyright 2016 The Chromium Authors |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef BASE_TYPES_ID_TYPE_H_ |
| #define BASE_TYPES_ID_TYPE_H_ |
| |
| #include <cstdint> |
| #include <type_traits> |
| |
| #include "base/ranges/algorithm.h" |
| #include "base/types/strong_alias.h" |
| |
| namespace base { |
| |
| // A specialization of StrongAlias for integer-based identifiers. |
| // |
| // IdType32<>, IdType64<>, etc. wrap an integer id in a custom, type-safe type. |
| // |
| // IdType32<Foo> is an alternative to int, for a class Foo with methods like: |
| // |
| // int GetId() { return id_; }; |
| // static Foo* FromId(int id) { return g_all_foos_by_id[id]; } |
| // |
| // Such methods are a standard means of safely referring to objects across |
| // thread and process boundaries. But if a nearby class Bar also represents |
| // its IDs as a bare int, horrific mixups are possible -- one example, of many, |
| // is http://crrev.com/365437. IdType<> offers compile-time protection against |
| // such mishaps, since IdType32<Foo> is incompatible with IdType32<Bar>, even |
| // though both just compile down to an int32_t. |
| // |
| // Templates in this file: |
| // IdType32<T> / IdTypeU32<T>: Signed / unsigned 32-bit IDs |
| // IdType64<T> / IdTypeU64<T>: Signed / unsigned 64-bit IDs |
| // IdType<>: For when you need a different underlying type or |
| // default/null values other than zero. |
| // |
| // IdType32<Foo> behaves just like an int32_t in the following aspects: |
| // - it can be used as a key in std::map; |
| // - it can be used as a key in std::unordered_map (see StrongAlias::Hasher); |
| // - it can be used as an argument to DCHECK_EQ or streamed to LOG(ERROR); |
| // - it has the same memory footprint and runtime overhead as int32_t; |
| // - it can be copied by memcpy. |
| // - it can be used in IPC messages. |
| // |
| // IdType32<Foo> has the following differences from a bare int32_t: |
| // - it forces coercions to go through the explicit constructor and value() |
| // getter; |
| // - it restricts the set of available operations (e.g. no multiplication); |
| // - it default-constructs to a null value and allows checking against the null |
| // value via is_null method. |
| // - optionally it may have additional values that are all considered null. |
| template <typename TypeMarker, |
| typename WrappedType, |
| WrappedType kInvalidValue, |
| WrappedType kFirstGeneratedId = kInvalidValue + 1, |
| WrappedType... kExtraInvalidValues> |
| class IdType : public StrongAlias<TypeMarker, WrappedType> { |
| public: |
| static constexpr WrappedType kAllInvalidValues[] = {kInvalidValue, |
| kExtraInvalidValues...}; |
| |
| static_assert(std::is_unsigned_v<WrappedType> || |
| base::ranges::all_of(kAllInvalidValues, |
| [](WrappedType v) { return v <= 0; }), |
| "If signed, invalid values should be negative or equal to zero " |
| "to avoid overflow issues."); |
| |
| static_assert(base::ranges::all_of(kAllInvalidValues, |
| [](WrappedType v) { |
| return kFirstGeneratedId != v; |
| }), |
| "The first generated ID cannot be invalid."); |
| |
| static_assert(std::is_unsigned_v<WrappedType> || |
| base::ranges::all_of(kAllInvalidValues, |
| [](WrappedType v) { |
| return kFirstGeneratedId > v; |
| }), |
| "If signed, the first generated ID must be greater than all " |
| "invalid values so that the monotonically increasing " |
| "GenerateNextId method will never return an invalid value."); |
| |
| using StrongAlias<TypeMarker, WrappedType>::StrongAlias; |
| |
| // This class can be used to generate unique IdTypes. It keeps an internal |
| // counter that is continually increased by one every time an ID is generated. |
| class Generator { |
| public: |
| Generator() = default; |
| |
| // Generates the next unique ID. |
| IdType GenerateNextId() { return FromUnsafeValue(next_id_++); } |
| |
| // Non-copyable. |
| Generator(const Generator&) = delete; |
| Generator& operator=(const Generator&) = delete; |
| |
| private: |
| WrappedType next_id_ = kFirstGeneratedId; |
| }; |
| |
| // Default-construct in the null state. |
| constexpr IdType() |
| : StrongAlias<TypeMarker, WrappedType>::StrongAlias(kInvalidValue) {} |
| |
| constexpr bool is_null() const { |
| return base::ranges::any_of(kAllInvalidValues, [this](WrappedType value) { |
| return this->value() == value; |
| }); |
| } |
| |
| constexpr explicit operator bool() const { return !is_null(); } |
| |
| // TODO(mpawlowski) Replace these with constructor/value() getter. The |
| // conversions are safe as long as they're explicit (which is taken care of by |
| // StrongAlias). |
| constexpr static IdType FromUnsafeValue(WrappedType value) { |
| return IdType(value); |
| } |
| constexpr WrappedType GetUnsafeValue() const { return this->value(); } |
| }; |
| |
| // Type aliases for convenience: |
| template <typename TypeMarker> |
| using IdType32 = IdType<TypeMarker, std::int32_t, 0>; |
| template <typename TypeMarker> |
| using IdTypeU32 = IdType<TypeMarker, std::uint32_t, 0>; |
| template <typename TypeMarker> |
| using IdType64 = IdType<TypeMarker, std::int64_t, 0>; |
| template <typename TypeMarker> |
| using IdTypeU64 = IdType<TypeMarker, std::uint64_t, 0>; |
| |
| } // namespace base |
| |
| #endif // BASE_TYPES_ID_TYPE_H_ |