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<spanstream>: Fix ambiguity among constructors of basic_ispanstream #5309

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Merged
Stephan T. Lavavej (StephanTLavavej) merged 1 commit into from
Feb 25, 2025
Merged

<spanstream>: Fix ambiguity among constructors of basic_ispanstream #5309

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13 changes: 8 additions & 5 deletions stl/inc/spanstream
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Original file line number Diff line number Diff line change
Expand Up @@ -190,6 +190,11 @@ void swap(basic_spanbuf<_Elem, _Traits>& _Left, basic_spanbuf<_Elem, _Traits>& _
_Left.swap(_Right);
}

template <class _Elem, size_t _Extent>
span<_Elem, _Extent> _As_nonconst_span(const span<const _Elem, _Extent> _Span) noexcept {
return span<_Elem, _Extent>{const_cast<_Elem*>(_Span.data()), _Span.size()};
}

_EXPORT_STD template <class _Elem, class _Traits>
class basic_ispanstream : public basic_istream<_Elem, _Traits> {
private:
Expand All @@ -207,9 +212,6 @@ public:
explicit basic_ispanstream(_STD span<_Elem> _Span, ios_base::openmode _Which = ios_base::in)
: _Mybase(_STD addressof(_Buf)), _Buf(_Span, _Which | ios_base::in) {}

explicit basic_ispanstream(_STD span<const _Elem> _Span)
: basic_ispanstream(_STD span<_Elem>{const_cast<_Elem*>(_Span.data()), _Span.size()}) {}

basic_ispanstream(const basic_ispanstream&) = delete;

basic_ispanstream(basic_ispanstream&& _Right) : _Mybase(_STD move(_Right)), _Buf(_STD move(_Right._Buf)) {
Expand All @@ -220,7 +222,8 @@ public:
requires (
!convertible_to<_ReadOnlyRange, _STD span<_Elem>> && convertible_to<_ReadOnlyRange, _STD span<const _Elem>>)
explicit basic_ispanstream(_ReadOnlyRange&& _Range)
: basic_ispanstream(static_cast<_STD span<const _Elem>>(_STD forward<_ReadOnlyRange>(_Range))) {}
: basic_ispanstream(
_STD _As_nonconst_span(static_cast<_STD span<const _Elem>>(_STD forward<_ReadOnlyRange>(_Range)))) {}

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

Expand Down Expand Up @@ -254,7 +257,7 @@ public:
!convertible_to<_ReadOnlyRange, _STD span<_Elem>> && convertible_to<_ReadOnlyRange, _STD span<const _Elem>>)
void span(_ReadOnlyRange&& _Range) noexcept {
const auto _Sp = static_cast<_STD span<const _Elem>>(_STD forward<_ReadOnlyRange>(_Range));
this->span(_STD span<_Elem>{const_cast<_Elem*>(_Sp.data()), _Sp.size()});
rdbuf()->span(_STD _As_nonconst_span(_Sp));
}

private:
Expand Down
22 changes: 22 additions & 0 deletions tests/std/tests/P0448R4_spanstream/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -674,6 +674,28 @@ void test_ispanstream() {
assert(static_cast<test_buf*>(special_range_constructed.rdbuf())->epptr() == nullptr);
}

{ // GH-5308: <spanstream>: Constructing ispanstream from string no longer compiles since VS 17.13
basic_string<CharT> str(42, static_cast<CharT>('*'));
basic_ispanstream<CharT> from_string_constructed{str};
assert(from_string_constructed.span().data() == str.data());
assert(static_cast<test_buf*>(from_string_constructed.rdbuf())->eback() == str.data());
assert(static_cast<test_buf*>(from_string_constructed.rdbuf())->gptr() == str.data());
assert(static_cast<test_buf*>(from_string_constructed.rdbuf())->egptr() == str.data() + str.size());
assert(static_cast<test_buf*>(from_string_constructed.rdbuf())->pbase() == nullptr);
assert(static_cast<test_buf*>(from_string_constructed.rdbuf())->pptr() == nullptr);
assert(static_cast<test_buf*>(from_string_constructed.rdbuf())->epptr() == nullptr);

basic_ispanstream<CharT> from_string_reset{span<CharT>{}};
from_string_reset.span(str);
assert(from_string_reset.span().data() == str.data());
assert(static_cast<test_buf*>(from_string_reset.rdbuf())->eback() == str.data());
assert(static_cast<test_buf*>(from_string_reset.rdbuf())->gptr() == str.data());
assert(static_cast<test_buf*>(from_string_reset.rdbuf())->egptr() == str.data() + str.size());
assert(static_cast<test_buf*>(from_string_reset.rdbuf())->pbase() == nullptr);
assert(static_cast<test_buf*>(from_string_reset.rdbuf())->pptr() == nullptr);
assert(static_cast<test_buf*>(from_string_reset.rdbuf())->epptr() == nullptr);
}

{ // span
CharT buffer[10];
basic_ispanstream<CharT> is{span<CharT>{buffer}};
Expand Down