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