78 lines
2.3 KiB
C
78 lines
2.3 KiB
C
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#pragma once
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#include <cstddef>
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#include <functional>
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#include <utility>
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namespace c10 {
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/**
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* This template simplifies generation of simple classes that wrap an id
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* in a typesafe way. Namely, you can use it to create a very lightweight
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* type that only offers equality comparators and hashing. Example:
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*
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* struct MyIdType final : IdWrapper<MyIdType, uint32_t> {
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* constexpr explicit MyIdType(uint32_t id): IdWrapper(id) {}
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* };
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*
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* Then in the global top level namespace:
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*
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* C10_DEFINE_HASH_FOR_IDWRAPPER(MyIdType);
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*
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* That's it - equality operators and hash functions are automatically defined
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* for you, given the underlying type supports it.
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*/
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template <class ConcreteType, class UnderlyingType>
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class IdWrapper {
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public:
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using underlying_type = UnderlyingType;
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using concrete_type = ConcreteType;
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protected:
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constexpr explicit IdWrapper(underlying_type id) noexcept(
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noexcept(underlying_type(std::declval<underlying_type>())))
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: id_(id) {}
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constexpr underlying_type underlyingId() const
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noexcept(noexcept(underlying_type(std::declval<underlying_type>()))) {
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return id_;
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}
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private:
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friend size_t hash_value(const concrete_type& v) {
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return std::hash<underlying_type>()(v.id_);
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}
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// TODO Making operator== noexcept if underlying type is noexcept equality
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// comparable doesn't work with GCC 4.8.
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// Fix this once we don't need GCC 4.8 anymore.
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friend constexpr bool operator==(
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const concrete_type& lhs,
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const concrete_type& rhs) noexcept {
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return lhs.id_ == rhs.id_;
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}
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// TODO Making operator!= noexcept if operator== is noexcept doesn't work with
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// GCC 4.8.
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// Fix this once we don't need GCC 4.8 anymore.
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friend constexpr bool operator!=(
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const concrete_type& lhs,
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const concrete_type& rhs) noexcept {
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return !(lhs == rhs);
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}
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underlying_type id_;
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};
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} // namespace c10
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#define C10_DEFINE_HASH_FOR_IDWRAPPER(ClassName) \
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namespace std { \
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template <> \
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struct hash<ClassName> { \
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size_t operator()(ClassName x) const { \
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return hash_value(x); \
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} \
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}; \
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}
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