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

[Patrick Palka]

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});

which works generally for any range 'c' (of integers).  But either
approach works for me.  LGTM either way.

>  
>  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
> 
>