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[libc++][syncbuf] Implements LWG3253. #99778

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Merged
merged 1 commit into from
Aug 30, 2024
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[libc++][syncbuf] Implements LWG3253. #99778

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2 changes: 1 addition & 1 deletion libcxx/docs/Status/Cxx20Issues.csv
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Original file line number Diff line number Diff line change
Expand Up @@ -172,7 +172,7 @@
"`LWG3221 <https://wg21.link/LWG3221>`__","Result of ``year_month``\ arithmetic with ``months``\ is ambiguous","2019-11 (Belfast)","|Complete|","8.0",""
"`LWG3235 <https://wg21.link/LWG3235>`__","``parse``\ manipulator without abbreviation is not callable","2019-11 (Belfast)","","",""
"`LWG3246 <https://wg21.link/LWG3246>`__","LWG3246: What are the constraints on the template parameter of `basic_format_arg`?","2019-11 (Belfast)","|Nothing To Do|","",""
"`LWG3253 <https://wg21.link/LWG3253>`__","``basic_syncbuf::basic_syncbuf()``\ should not be explicit","2019-11 (Belfast)","","",""
"`LWG3253 <https://wg21.link/LWG3253>`__","``basic_syncbuf::basic_syncbuf()``\ should not be explicit","2019-11 (Belfast)","|Complete|","20.0",""
"`LWG3245 <https://wg21.link/LWG3245>`__","Unnecessary restriction on ``'%p'``\ parse specifier","2019-11 (Belfast)","","",""
"`LWG3244 <https://wg21.link/LWG3244>`__","Constraints for ``Source``\ in |sect|\ [fs.path.req] insufficiently constrainty","2019-11 (Belfast)","","",""
"`LWG3241 <https://wg21.link/LWG3241>`__","``chrono-spec``\ grammar ambiguity in |sect|\ [time.format]","2019-11 (Belfast)","|Complete|","16.0",""
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9 changes: 7 additions & 2 deletions libcxx/include/syncstream
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Original file line number Diff line number Diff line change
Expand Up @@ -46,7 +46,9 @@ namespace std {
using streambuf_type = basic_streambuf<charT, traits>;

// [syncstream.syncbuf.cons], construction and destruction
explicit basic_syncbuf(streambuf_type* obuf = nullptr)
basic_syncbuf()
: basic_syncbuf(nullptr) {}
explicit basic_syncbuf(streambuf_type* obuf)
: basic_syncbuf(obuf, Allocator()) {}
basic_syncbuf(streambuf_type*, const Allocator&);
basic_syncbuf(basic_syncbuf&&);
Expand Down Expand Up @@ -253,7 +255,10 @@ public:

// [syncstream.syncbuf.cons], construction and destruction

_LIBCPP_HIDE_FROM_ABI explicit basic_syncbuf(streambuf_type* __obuf = nullptr)
_LIBCPP_HIDE_FROM_ABI basic_syncbuf()
: basic_syncbuf(nullptr) {}
Comment on lines +258 to +259
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I think it's possible to test this. Before applying the LWG issue resolution, the following code would not have compiled:

basic_syncbuf f() {
  return {};
}

But after the LWG issue resolution, this compiles because the default constructor is not explicit. So I think a test like this should work:

basic_syncbuf buf = {};

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I like the return {} test better, so went that direction for the test.


_LIBCPP_HIDE_FROM_ABI explicit basic_syncbuf(streambuf_type* __obuf)
: basic_syncbuf(__obuf, _Allocator()) {}

_LIBCPP_HIDE_FROM_ABI basic_syncbuf(streambuf_type* __obuf, _Allocator const& __alloc)
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7 changes: 7 additions & 0 deletions ...xx/test/std/input.output/syncstream/syncbuf/syncstream.syncbuf.cons/cons.default.pass.cpp
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Expand Up @@ -25,8 +25,15 @@
#include "constexpr_char_traits.h"
#include "test_allocator.h"

template <class CharT>
std::basic_syncbuf<CharT> lwg3253_default_constructor_is_not_explicit() {
return {};
}

template <class CharT>
void test() {
lwg3253_default_constructor_is_not_explicit<CharT>();

{
using Buf = std::basic_syncbuf<CharT>;
static_assert(std::default_initializable<Buf>);
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