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<optional>: Don't zero storage in default constructor #878

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Merged
CaseyCarter merged 3 commits into from
Jun 11, 2020
Merged

<optional>: Don't zero storage in default constructor #878

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<optional>: Don't zero storage in default constructor
CaseyCarter Jun 4, 2020
c1a452d
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CaseyCarter Jun 5, 2020
a30a798
Derp - fix what I broke
CaseyCarter Jun 9, 2020
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15 changes: 11 additions & 4 deletions stl/inc/optional
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Original file line number Diff line number Diff line change
Expand Up @@ -53,10 +53,17 @@ protected:
_THROW(bad_optional_access{});
}

struct _Nontrivial_dummy_type {
constexpr _Nontrivial_dummy_type() noexcept {
// This default constructor is user-provided to avoid zero-initialization when objects are value-initialized.
}
};
_STL_INTERNAL_STATIC_ASSERT(!is_trivially_default_constructible_v<_Nontrivial_dummy_type>);

template <class _Ty, bool = is_trivially_destructible_v<_Ty>>
struct _Optional_destruct_base { // either contains a value of _Ty or is empty (trivial destructor)
union {
char _Dummy;
_Nontrivial_dummy_type _Dummy;
remove_const_t<_Ty> _Value;
};
bool _Has_value;
Expand All @@ -75,7 +82,7 @@ struct _Optional_destruct_base { // either contains a value of _Ty or is empty (
template <class _Ty>
struct _Optional_destruct_base<_Ty, false> { // either contains a value of _Ty or is empty (non-trivial destructor)
union {
char _Dummy;
_Nontrivial_dummy_type _Dummy;
remove_const_t<_Ty> _Value;
};
bool _Has_value;
Expand Down Expand Up @@ -164,8 +171,8 @@ public:
using value_type = _Ty;

// constructors [optional.object.ctor]
constexpr optional() noexcept : _Mybase{} {}
constexpr optional(nullopt_t) noexcept : _Mybase{} {}
constexpr optional() noexcept {}
constexpr optional(nullopt_t) noexcept {}

template <class... _Types, enable_if_t<is_constructible_v<_Ty, _Types...>, int> = 0>
constexpr explicit optional(in_place_t, _Types&&... _Args) : _Mybase(in_place, _STD forward<_Types>(_Args)...) {}
Expand Down