[libcxx] Remove swap for std::span

[jdoerrie]

Summary

This change removes both the member function swap and the free function overload of swap for std::span. While swap is a member and overloaded for every other container in the standard library [1], it is neither a member function nor a free function overload for std::span [2]. Thus the corresponding implementation should be removed.

[1] https://eel.is/c++draft/libraryindex#:swap
[2] https://eel.is/c++draft/span.overview

[jdoerrie]

Friendly ping

[miscco]

That is indeed the correct thing to do +1

[ldionne]

@mclow.lists Can you comment on why you included these functions?

This seems right to me.

[ldionne]

Requesting changes just so it shows up in my review queue.

[ldionne]

@jdoerrie @miscco Let's move forward with this.

[ldionne]

Please make sure this is rebased on master.

[jdoerrie]

Rebase

[jdoerrie]

Thanks, Louis! I rebased the diff on the latest master. Could you land the patch for me? I believe I lack the required permissions to do this myself.

[ldionne]

What "Author Name <[e-mail]>" should I use for the commit?

[jdoerrie]

"Jan Wilken Dörrie <[e-mail]>" works for me :)

libcxx/include/span

//  ~span() noexcept = default;
     _LIBCPP_INLINE_VISIBILITY constexpr pointer data()                         const noexcept { return __data; }
 
 // [span.iter], span iterator support
     _LIBCPP_INLINE_VISIBILITY constexpr iterator                 begin() const noexcept { return iterator(data()); }
     _LIBCPP_INLINE_VISIBILITY constexpr iterator                   end() const noexcept { return iterator(data() + size()); }
     _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator        rbegin() const noexcept { return reverse_iterator(end()); }
     _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator          rend() const noexcept { return reverse_iterator(begin()); }
 
-    _LIBCPP_INLINE_VISIBILITY constexpr void swap(span &__other) noexcept
-    {
-        pointer __p = __data;
-        __data = __other.__data;
-        __other.__data = __p;
-    }
-
     _LIBCPP_INLINE_VISIBILITY span<const byte, _Extent * sizeof(element_type)> __as_bytes() const noexcept
     { return span<const byte, _Extent * sizeof(element_type)>{reinterpret_cast<const byte *>(data()), size_bytes()}; }
 
     _LIBCPP_INLINE_VISIBILITY span<byte, _Extent * sizeof(element_type)> __as_writable_bytes() const noexcept
     { return span<byte, _Extent * sizeof(element_type)>{reinterpret_cast<byte *>(data()), size_bytes()}; }
 
 private:
     pointer    __data;
//    ~span() noexcept = default;
     _LIBCPP_INLINE_VISIBILITY constexpr pointer data()                         const noexcept { return __data; }
 
 // [span.iter], span iterator support
     _LIBCPP_INLINE_VISIBILITY constexpr iterator                 begin() const noexcept { return iterator(data()); }
     _LIBCPP_INLINE_VISIBILITY constexpr iterator                   end() const noexcept { return iterator(data() + size()); }
     _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator        rbegin() const noexcept { return reverse_iterator(end()); }
     _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator          rend() const noexcept { return reverse_iterator(begin()); }
 
-    _LIBCPP_INLINE_VISIBILITY constexpr void swap(span &__other) noexcept
-    {
-        pointer __p = __data;
-        __data = __other.__data;
-        __other.__data = __p;
-
-        size_type __sz = __size;
-        __size = __other.__size;
-        __other.__size = __sz;
-    }
-
     _LIBCPP_INLINE_VISIBILITY span<const byte, dynamic_extent> __as_bytes() const noexcept
     { return {reinterpret_cast<const byte *>(data()), size_bytes()}; }
 
     _LIBCPP_INLINE_VISIBILITY span<byte, dynamic_extent> __as_writable_bytes() const noexcept
     { return {reinterpret_cast<byte *>(data()), size_bytes()}; }
 
 private:
     pointer   __data;
     size_type __size;
 };
 
 //  as_bytes & as_writable_bytes
 template <class _Tp, size_t _Extent>
 _LIBCPP_INLINE_VISIBILITY
 auto as_bytes(span<_Tp, _Extent> __s) noexcept
 -> decltype(__s.__as_bytes())
 { return    __s.__as_bytes(); }
 
 template <class _Tp, size_t _Extent>
 _LIBCPP_INLINE_VISIBILITY
 auto as_writable_bytes(span<_Tp, _Extent> __s) noexcept
 -> enable_if_t<!is_const_v<_Tp>, decltype(__s.__as_writable_bytes())>
 { return __s.__as_writable_bytes(); }
 
-template <class _Tp, size_t _Extent>
-_LIBCPP_INLINE_VISIBILITY
-constexpr void swap(span<_Tp, _Extent> &__lhs, span<_Tp, _Extent> &__rhs) noexcept
-{ __lhs.swap(__rhs); }
-
-
 //  Deduction guides
 template<class _Tp, size_t _Sz>
     span(_Tp (&)[_Sz]) -> span<_Tp, _Sz>;
 
 template<class _Tp, size_t _Sz>
     span(array<_Tp, _Sz>&) -> span<_Tp, _Sz>;
 
 template<class _Tp, size_t _Sz>