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[libc++] Address post-commit comments for __scope_guard #116291

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Nov 16, 2024
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[libc++] Address post-commit comments for __scope_guard #116291

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18 changes: 7 additions & 11 deletions libcxx/include/__utility/scope_guard.h
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Original file line number Diff line number Diff line change
Expand Up @@ -26,26 +26,22 @@ _LIBCPP_BEGIN_NAMESPACE_STD
template <class _Func>
class __scope_guard {
_Func __func_;
bool __moved_from_;

public:
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __scope_guard(_Func __func) : __func_(std::move(__func)) {}
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __scope_guard(_Func __func) : __func_(std::move(__func)) {}
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 ~__scope_guard() { __func_(); }

__scope_guard(const __scope_guard&) = delete;
__scope_guard(const __scope_guard&) = delete;
__scope_guard& operator=(const __scope_guard&) = delete;
__scope_guard& operator=(__scope_guard&&) = delete;

// C++17 has mandatory RVO, so we don't need the move constructor anymore to make __make_scope_guard work.
// C++14 doesn't have mandatory RVO, so we have to provide a declaration even though no compiler will ever generate
// a call to the move constructor.
#if _LIBCPP_STD_VER <= 14
__scope_guard(__scope_guard&& __other) : __func_(__other.__func_) {
_LIBCPP_ASSERT_INTERNAL(!__other.__moved_from_, "Cannot move twice from __scope_guard");
__other.__moved_from_ = true;
}
__scope_guard(__scope_guard&&);
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@philnik777 philnik777 Nov 14, 2024

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I'm not sure whether this approach is better than having dead code. @ldionne thoughts?

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@ldionne ldionne Nov 14, 2024

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Oh, I like this a lot better than the previous approach. There's not much harm in providing this private declaration.

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@philnik777 philnik777 Nov 14, 2024

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Uh... this actually has to be public. Sometimes my brain just turns off. Does that change your thoughts on this?

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@ldionne ldionne Nov 14, 2024

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It doesn't, but thanks for checking.

#else
__scope_guard(__scope_guard&&) = delete;
#endif

__scope_guard& operator=(const __scope_guard&) = delete;
__scope_guard& operator=(__scope_guard&&) = delete;
};

template <class _Func>
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