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P0966R1 string::reserve() should not shrink #176

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merged 2 commits into from Oct 17, 2019
Merged

P0966R1 string::reserve() should not shrink #176

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ab11d3b
P0966R1 string::reserve() should not shrink
NathanSWard Oct 15, 2019
dc16125
PR: requested changes implemented
NathanSWard Oct 16, 2019
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20 changes: 20 additions & 0 deletions stl/inc/xstring
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Expand Up @@ -3616,6 +3616,25 @@ public:
return _Mypair._Myval2._Myres;
}

#if _HAS_CXX20
void reserve(_CRT_GUARDOVERFLOW const size_type _Newcap) { // determine new minimum length of allocated storage
if (_Mypair._Myval2._Myres < _Newcap) { // reallocate to grow
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const size_type _Old_size = _Mypair._Myval2._Mysize;
_Reallocate_grow_by(
_Newcap - _Old_size, [](_Elem* const _New_ptr, const _Elem* const _Old_ptr, const size_type _Old_size) {
_Traits::copy(_New_ptr, _Old_ptr, _Old_size + 1);
});

_Mypair._Myval2._Mysize = _Old_size;
return;
}

// ignore requests to reserve to [0, _Myres]
}

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_CXX20_DEPRECATE_STRING_RESERVE_DEFAULT_ARGUMENT void reserve() {} // no-op
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#else // _HAS_CXX20
void reserve(_CRT_GUARDOVERFLOW const size_type _Newcap = 0) { // determine new minimum length of allocated storage
if (_Mypair._Myval2._Mysize > _Newcap) { // requested capacity is not large enough for current size, ignore
return; // nothing to do
Expand Down Expand Up @@ -3644,6 +3663,7 @@ public:

// ignore requests to reserve to [_BUF_SIZE, _Myres)
}
#endif // _HAS_CXX20

_NODISCARD bool empty() const noexcept {
return size() == 0;
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16 changes: 15 additions & 1 deletion stl/inc/yvals_core.h
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Expand Up @@ -799,7 +799,21 @@
#define _DEPRECATE_STDEXT_HASH_UPPER_BOUND
#endif // ^^^ warning disabled ^^^

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// next warning number: STL4024
// P0966R1 [depr.string.capacity]
#if _HAS_CXX20 && !defined(_SILENCE_CXX20_STRING_RESERVE_DEFAULT_ARGUMENT_DEPRECATION_WARNING) \
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&& !defined(_SILENCE_ALL_CXX20_DEPRECATION_WARNINGS)
#define _CXX20_DEPRECATE_STRING_RESERVE_DEFAULT_ARGUMENT \
[[deprecated("warning STL4024: " \
"std::string::reserve() with the default arument 0 is deprecated in C++20. " \
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"If the intention is to shrink the string's capacity, use std::string::shrink_to_fit(). Otherwise, "\
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"provide an argument to std::string::reserve(). " \
"You can define _SILENCE_CXX20_STRING_RESERVE_DEFAULT_ARGUMENT_DEPRECATION_WARNING" \
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"or _SILENCE_ALL_CXX20_DEPRECATION_WARNINGS to acknowledge that you have received this warning.")]]
#else // ^^^ warning enabled / warning disabled vvv
#define _CXX20_DEPRECATE_STRING_RESERVE_DEFAULT_ARGUMENT
#endif // ^^^ warning disabled ^^^

// next warning number: STL4025


// LIBRARY FEATURE-TEST MACROS
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