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#ifndef AL_OPTIONAL_H
#define AL_OPTIONAL_H
#include <initializer_list>
#include <type_traits>
#include <utility>
#include "almalloc.h"
namespace al {
#define REQUIRES(...) bool rt_=true, std::enable_if_t<rt_ && (__VA_ARGS__),bool> = true
struct nullopt_t { };
struct in_place_t { };
constexpr nullopt_t nullopt{};
constexpr in_place_t in_place{};
template<typename T>
class optional {
bool mHasValue{false};
union {
char mDummy[sizeof(T)]{};
T mValue;
};
template<typename... Args>
void DoConstruct(Args&& ...args)
{
::new (std::addressof(mValue)) T{std::forward<Args>(args)...};
mHasValue = true;
}
public:
using value_type = T;
optional() noexcept = default;
optional(nullopt_t) noexcept { }
template<REQUIRES(std::is_copy_constructible<T>::value)>
optional(const optional &rhs) { if(rhs) DoConstruct(*rhs); }
template<REQUIRES(std::is_move_constructible<T>::value)>
optional(optional&& rhs) { if(rhs) DoConstruct(std::move(*rhs)); }
template<typename... Args, REQUIRES(std::is_constructible<T, Args...>::value)>
explicit optional(in_place_t, Args&& ...args) : mHasValue{true}
, mValue{std::forward<Args>(args)...}
{ }
~optional() { if(mHasValue) al::destroy_at(std::addressof(mValue)); }
optional& operator=(nullopt_t) noexcept { reset(); return *this; }
std::enable_if_t<std::is_copy_constructible<T>::value && std::is_copy_assignable<T>::value,
optional&> operator=(const optional &rhs)
{
if(!rhs)
reset();
else if(*this)
mValue = *rhs;
else
DoConstruct(*rhs);
return *this;
}
std::enable_if_t<std::is_move_constructible<T>::value && std::is_move_assignable<T>::value,
optional&> operator=(optional&& rhs)
{
if(!rhs)
reset();
else if(*this)
mValue = std::move(*rhs);
else
DoConstruct(std::move(*rhs));
return *this;
}
template<typename U=T>
std::enable_if_t<std::is_constructible<T, U>::value &&
std::is_assignable<T&, U>::value &&
!std::is_same<typename std::decay<U>::type, optional<T>>::value &&
(!std::is_same<typename std::decay<U>::type, T>::value ||
!std::is_scalar<U>::value),
optional&> operator=(U&& rhs)
{
if(*this)
mValue = std::forward<U>(rhs);
else
DoConstruct(std::forward<U>(rhs));
return *this;
}
const T* operator->() const { return std::addressof(mValue); }
T* operator->() { return std::addressof(mValue); }
const T& operator*() const& { return mValue; }
T& operator*() & { return mValue; }
const T&& operator*() const&& { return std::move(mValue); }
T&& operator*() && { return std::move(mValue); }
operator bool() const noexcept { return mHasValue; }
bool has_value() const noexcept { return mHasValue; }
T& value() & { return mValue; }
const T& value() const& { return mValue; }
T&& value() && { return std::move(mValue); }
const T&& value() const&& { return std::move(mValue); }
template<typename U>
T value_or(U&& defval) const&
{ return bool{*this} ? **this : static_cast<T>(std::forward<U>(defval)); }
template<typename U>
T value_or(U&& defval) &&
{ return bool{*this} ? std::move(**this) : static_cast<T>(std::forward<U>(defval)); }
void reset() noexcept
{
if(mHasValue)
al::destroy_at(std::addressof(mValue));
mHasValue = false;
}
};
template<typename T>
inline optional<std::decay_t<T>> make_optional(T&& arg)
{ return optional<std::decay_t<T>>{in_place, std::forward<T>(arg)}; }
template<typename T, typename... Args>
inline optional<T> make_optional(Args&& ...args)
{ return optional<T>{in_place, std::forward<Args>(args)...}; }
template<typename T, typename U, typename... Args>
inline optional<T> make_optional(std::initializer_list<U> il, Args&& ...args)
{ return optional<T>{in_place, il, std::forward<Args>(args)...}; }
#undef REQUIRES
} // namespace al
#endif /* AL_SPAN_H */
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