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//===-- Standalone implementation std::optional -----------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_LIBC_SRC_SUPPORT_CPP_OPTIONAL_H
#define LLVM_LIBC_SRC_SUPPORT_CPP_OPTIONAL_H
namespace __llvm_libc {
namespace cpp {
// Trivial nullopt_t struct.
struct nullopt_t {};
// nullopt that can be used and returned
inline constexpr nullopt_t nullopt;
// This is very simple implementation of the std::optional class. There are a
// number of guarantees in the standard that are not made here.
//
// This class will be extended as needed in future.
//
// T currently needs to be a scalar or an object with the following properties:
// - copy constructible
// - copy assignable
// - destructible
template <class T> class optional {
template <class E> class OptionalStorage {
public:
union {
E StoredValue;
char Placeholder;
};
bool InUse = false;
OptionalStorage() : Placeholder(0), InUse(false) {}
OptionalStorage(const E &t) : StoredValue(t), InUse(true) {}
~OptionalStorage() {
if (InUse)
StoredValue.~E();
}
void reset() {
if (InUse)
StoredValue.~E();
InUse = false;
}
};
OptionalStorage<T> Storage;
public:
optional() {}
optional(nullopt_t) {}
optional(const T &t) : Storage(t) {}
T value() const { return Storage.StoredValue; }
bool has_value() const { return Storage.InUse; }
void reset() { Storage.reset(); }
constexpr explicit operator bool() const { return Storage.InUse; }
constexpr optional &operator=(nullopt_t) {
reset();
return *this;
}
constexpr T &operator*() & { return Storage.StoredValue; }
constexpr const T &operator*() const & { return Storage.StoredValue; }
constexpr T *operator->() { return &Storage.StoredValue; }
constexpr const T *operator->() const { return &Storage.StoredValue; }
};
} // namespace cpp
} // namespace __llvm_libc
#endif // LLVM_LIBC_SRC_SUPPORT_CPP_OPTIONAL_H
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