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//===-- Standalone implementation of 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
#include "src/__support/CPP/type_traits.h"
#include "src/__support/CPP/utility.h"
#include "src/__support/macros/attributes.h"
namespace LIBC_NAMESPACE {
namespace cpp {
// Trivial nullopt_t struct.
struct nullopt_t {
LIBC_INLINE constexpr explicit nullopt_t() = default;
};
// nullopt that can be used and returned.
LIBC_INLINE_VAR constexpr nullopt_t nullopt{};
// This is very simple implementation of the std::optional class. It makes
// several assumptions that the underlying type is trivially constructable,
// copyable, or movable.
template <typename T> class optional {
template <typename U, bool = !is_trivially_destructible<U>::value>
struct OptionalStorage {
union {
char empty;
U stored_value;
};
LIBC_INLINE ~OptionalStorage() { stored_value.~U(); }
LIBC_INLINE constexpr OptionalStorage() : empty() {}
template <typename... Args>
LIBC_INLINE constexpr explicit OptionalStorage(in_place_t, Args &&...args)
: stored_value(forward<Args>(args)...) {}
};
template <typename U> struct OptionalStorage<U, false> {
union {
char empty;
U stored_value;
};
// The only difference is that this class doesn't have a destructor.
LIBC_INLINE constexpr OptionalStorage() : empty() {}
template <typename... Args>
LIBC_INLINE constexpr explicit OptionalStorage(in_place_t, Args &&...args)
: stored_value(forward<Args>(args)...) {}
};
OptionalStorage<T> storage;
bool in_use = false;
public:
LIBC_INLINE constexpr optional() = default;
LIBC_INLINE constexpr optional(nullopt_t) {}
LIBC_INLINE constexpr optional(const T &t)
: storage(in_place, t), in_use(true) {}
LIBC_INLINE constexpr optional(const optional &) = default;
LIBC_INLINE constexpr optional(T &&t)
: storage(in_place, move(t)), in_use(true) {}
LIBC_INLINE constexpr optional(optional &&O) = default;
template <typename... ArgTypes>
LIBC_INLINE constexpr optional(in_place_t, ArgTypes &&...Args)
: storage(in_place, forward<ArgTypes>(Args)...), in_use(true) {}
LIBC_INLINE constexpr optional &operator=(T &&t) {
storage = move(t);
return *this;
}
LIBC_INLINE constexpr optional &operator=(optional &&) = default;
LIBC_INLINE constexpr optional &operator=(const T &t) {
storage = t;
return *this;
}
LIBC_INLINE constexpr optional &operator=(const optional &) = default;
LIBC_INLINE constexpr void reset() {
if (in_use)
storage.~OptionalStorage();
in_use = false;
}
LIBC_INLINE constexpr const T &value() const & {
return storage.stored_value;
}
LIBC_INLINE constexpr T &value() & { return storage.stored_value; }
LIBC_INLINE constexpr explicit operator bool() const { return in_use; }
LIBC_INLINE constexpr bool has_value() const { return in_use; }
LIBC_INLINE constexpr const T *operator->() const {
return &storage.stored_value;
}
LIBC_INLINE constexpr T *operator->() { return &storage.stored_value; }
LIBC_INLINE constexpr const T &operator*() const & {
return storage.stored_value;
}
LIBC_INLINE constexpr T &operator*() & { return storage.stored_value; }
LIBC_INLINE constexpr T &&value() && { return move(storage.stored_value); }
LIBC_INLINE constexpr T &&operator*() && {
return move(storage.stored_value);
}
};
} // namespace cpp
} // namespace LIBC_NAMESPACE
#endif // LLVM_LIBC_SRC___SUPPORT_CPP_OPTIONAL_H
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