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Add a helper to construct the optional value

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This commit is contained in:
Chris Robinson
2019-07-01 17:34:02 -07:00
parent 6bb0edf0a5
commit bc1d058d2d
1 changed files with 18 additions and 29 deletions
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common/aloptional.h
+18 -29
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@@ -17,23 +17,28 @@ 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) : mHasValue{rhs.mHasValue}
{
if(mHasValue)
std::uninitialized_copy_n(std::addressof(*rhs), 1, std::addressof(mValue));
}
optional(const optional &rhs) { if(rhs) DoConstruct(*rhs); }
template<REQUIRES(std::is_move_constructible<T>::value)>
optional(optional&& rhs) : mHasValue{rhs.mHasValue}
{
if(mHasValue)
al::uninitialized_move_n(std::addressof(*rhs), 1, std::addressof(mValue));
}
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)...}
@@ -65,10 +70,7 @@ public:
else if(*this)
mValue = *rhs;
else
{
std::uninitialized_copy_n(std::addressof(*rhs), 1, std::addressof(mValue));
mHasValue = true;
}
DoConstruct(*rhs);
return *this;
}
template<REQUIRES(std::is_move_constructible<T>::value && std::is_move_assignable<T>::value)>
@@ -79,10 +81,7 @@ public:
else if(*this)
mValue = std::move(*rhs);
else
{
al::uninitialized_move_n(std::addressof(*rhs), 1, std::addressof(mValue));
mHasValue = true;
}
DoConstruct(std::move(*rhs));
return *this;
}
template<typename U=T, REQUIRES(std::is_constructible<T, U>::value &&
@@ -95,10 +94,7 @@ public:
if(*this)
mValue = std::forward<U>(rhs);
else
{
::new (std::addressof(mValue)) T{std::forward<U>(rhs)};
mHasValue = true;
}
DoConstruct(std::forward<U>(rhs));
return *this;
}
@@ -130,13 +126,6 @@ public:
al::destroy_at(std::addressof(mValue));
mHasValue = false;
}
private:
bool mHasValue{false};
union {
char mDummy[sizeof(T)]{};
T mValue;
};
};
template<typename T>