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// Copyright 2020 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_TOKEN_TYPE_H_
#define BASE_TYPES_TOKEN_TYPE_H_
#include <compare>
#include <type_traits>
#include <utility>
#include "base/check.h"
#include "base/types/strong_alias.h"
#include "base/unguessable_token.h"
namespace base {
// A specialization of StrongAlias for UnguessableToken. Unlike
// UnguessableToken, a TokenType<...> does not default to null and does not
// expose the concept of null tokens. If you need to indicate a null token,
// please use std::optional<TokenType<...>>.
template <typename TypeMarker>
class TokenType : public StrongAlias<TypeMarker, UnguessableToken> {
private:
using Super = StrongAlias<TypeMarker, UnguessableToken>;
public:
TokenType() : Super(UnguessableToken::Create()) {}
explicit TokenType(const UnguessableToken& token) : Super(token) {
// Disallow attempts to force a null UnguessableToken into a strongly-typed
// token. Allowing in-place nullability of UnguessableToken was a design
// mistake; do not propagate that mistake here as well.
CHECK(!token.is_empty());
}
// This object allows default assignment operators for compatibility with
// STL containers.
TokenType(const TokenType& token) = default;
TokenType(TokenType&& token) noexcept = default;
TokenType& operator=(const TokenType& token) = default;
TokenType& operator=(TokenType&& token) noexcept = default;
// StrongAlias doesn't define <=> because not all underlying types will
// implement it. TokenType can define it using UnguessableToken's
// implementation, though.
friend constexpr auto operator<=>(const TokenType& lhs,
const TokenType& rhs) {
return lhs.value() <=> rhs.value();
}
friend constexpr bool operator==(const TokenType& lhs, const TokenType& rhs) {
return lhs.value() == rhs.value();
}
template <typename H>
friend H AbslHashValue(H h, const TokenType& token_type) {
return H::combine(std::move(h), token_type.value());
}
// Hash functor for use in unordered containers.
struct Hasher {
using argument_type = TokenType;
using result_type = size_t;
result_type operator()(const argument_type& token) const {
return UnguessableTokenHash()(token.value());
}
};
// Mimic the UnguessableToken API for ease and familiarity of use.
std::string ToString() const { return this->value().ToString(); }
};
} // namespace base
#endif // BASE_TYPES_TOKEN_TYPE_H_
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