[PATCH] libstdc++: Support braces as arguments for std::erase on inplace_vector [PR121196]

[Tomasz Kaminski]

On Fri, Jul 25, 2025 at 4:57 PM Tomasz Kaminski <tkaminsk@redhat.com> wrote:

>
>
> On Fri, Jul 25, 2025 at 4:49 PM Patrick Palka <ppalka@redhat.com> wrote:
>
>> On Fri, 25 Jul 2025, Tomasz Kamiński wrote:
>>
>> >       PR libstdc++/121196
>> >
>> > libstdc++-v3/ChangeLog:
>> >
>> >       * include/std/inplace_vector (std::erase): Provide default
>> argument
>> >       for _Up parameter.
>> >       * testsuite/23_containers/inplace_vector/erasure.cc: Add test for
>> >       using braces-init-list as arguments to erase_if and use function
>> >       to verify content of inplace_vector
>> > ---
>> > I believe the actual fix (adding = _Tp) is trivial and could be commited
>> > without review. I have done more extensive changes to tests.
>> >
>> > Tested on x86_64-linux.
>> >
>> >  libstdc++-v3/include/std/inplace_vector       |  2 +-
>> >  .../23_containers/inplace_vector/erasure.cc   | 26 ++++++++++++++++---
>> >  2 files changed, 24 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/libstdc++-v3/include/std/inplace_vector
>> b/libstdc++-v3/include/std/inplace_vector
>> > index 290cf6eb0e9..b5a81bed3c9 100644
>> > --- a/libstdc++-v3/include/std/inplace_vector
>> > +++ b/libstdc++-v3/include/std/inplace_vector
>> > @@ -1354,7 +1354,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> >      }
>> >
>> >
>> > -  template<typename _Tp, size_t _Nm, typename _Up>
>> > +  template<typename _Tp, size_t _Nm, typename _Up = _Tp>
>> >      constexpr  size_t
>> >      erase(inplace_vector<_Tp, _Nm>& __cont, const _Up& __value)
>> >      {
>> > diff --git
>> a/libstdc++-v3/testsuite/23_containers/inplace_vector/erasure.cc
>> b/libstdc++-v3/testsuite/23_containers/inplace_vector/erasure.cc
>> > index c7fda097896..8fb56e90623 100644
>> > --- a/libstdc++-v3/testsuite/23_containers/inplace_vector/erasure.cc
>> > +++ b/libstdc++-v3/testsuite/23_containers/inplace_vector/erasure.cc
>> > @@ -2,18 +2,38 @@
>> >
>> >  #include <inplace_vector>
>> >  #include <testsuite_hooks.h>
>> > +#include <span>
>> > +
>> > +template<typename T, size_t N>
>> > +constexpr bool
>> > +eq(const std::inplace_vector<T, N>& l, std::span<const T> r) {
>> > +  if (l.size() != r.size())
>> > +    return false;
>> > +  for (auto i = 0u; i < l.size(); ++i)
>> > +    if (l[i] != r[i])
>> > +      return false;
>> > +  return true;
>> > +};
>>
>> Is this helper function to make the equality checks more concise?
>> I like to just use:
>>
>>   ranges::equal(c, (int[]){3, 6, 3});
>>
> I believe (int[]){...} is compound literal (
> https://en.cppreference.com/w/c/language/compound_literal.html)
> that is not supported in standard C++. GCC gives me warning on that:
> <source>:2:29: warning: ISO C++ forbids compound-literals [-Wpedantic]
> In C++ we could use:
> > using T = int[];
> > ranges::equal(c, T{3, 6, 3});
> Or in C++26 this should work, because span can be constructed from
> initializer_list:
> > ranges::equal(c, std::span{3, 6, 6});
> I will try to check that.
>
Because span constructor takes initializer_list<value_type> (i.e.
remove_cv_t<T>)
The deduction does not work. Also there is no CTAD.

>
> I just got this function copied from another test.
>
>>
>> which works generally for any range 'c' (of integers).  But either
>> approach works for me.  LGTM either way.
>>
> I ended up with something like follows:
VERIFY( std::ranges::equal(c, std::span<int const>({3, 6, 6}));
I think this obfuscates a the "meat" of the test with the sigils,
so I prefer keeping eq calls that are less verbose.


>
>> >
>> >  constexpr void
>> >  test_erase()
>> >  {
>> > -  std::inplace_vector<int, 15> c{1, 2, 3, 4, 5, 6, 5, 4, 3, 2, 1, 4,
>> 4, 9};
>> > +  std::inplace_vector<int, 15> c{1, 0, 3, 4, 5, 6, 5, 4, 3, 0, 1, 4,
>> 4, 9};
>> >    std::erase(c, 4);
>> >    VERIFY( c.size() == 10 );
>> >    std::erase(c, 1);
>> >    VERIFY( c.size() == 8 );
>> >    std::erase(c, 9);
>> >    VERIFY( c.size() == 7 );
>> > -  VERIFY( (c == std::inplace_vector<int, 15>{2, 3, 5, 6, 5, 3, 2}) );
>> > +  VERIFY( eq(c, {0, 3, 5, 6, 5, 3, 0}) );
>> > +
>> > +  std::erase(c, {});
>> > +  VERIFY( c.size() == 5 );
>> > +  VERIFY( eq(c, {3, 5, 6, 5, 3}) );
>> > +
>> > +  std::erase(c, {5});
>> > +  VERIFY( c.size() == 3 );
>> > +  VERIFY( eq(c, {3, 6, 3}) );
>> >
>> >    std::inplace_vector<int, 0> e;
>> >    std::erase(e, 10);
>> > @@ -29,7 +49,7 @@ test_erase_if()
>> >    std::erase_if(c, [](int i) { return i == 4; });
>> >    VERIFY( c.size() == 8 );
>> >    std::erase_if(c, [](int i) { return i & 1; });
>> > -  VERIFY( (c == std::inplace_vector<int, 15>{2, 2}) );
>> > +  VERIFY( eq(c, {2, 2}) );
>> >
>> >    std::inplace_vector<int, 0> e;
>> >    std::erase_if(e, [](int i) { return i > 5; });
>> > --
>> > 2.49.0
>> >
>> >
>
>
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