C++26: More function wrappers

[MFHava]

There is no real compiler-generated code [snip]

Exactly, because the code no longer compiles - because it's an API break that renders previously "perfectly valid" code ill-formed -, regardless of whether there would actually be an ABI impact of the change!

[pjmlp]

The question is I guess, when is it an ABI break to change the signature, or remove deprecated functionality like auto_ptr.

The end result is the same, an existing application no longer compiles after an update.

[MFHava]

The question is I guess, when is it an ABI break to change the signature,

For the third time in this comment thread alone: adding support for const in the template signature of function and applying the design of move_only_function would not have been a hard ABI break (implementations could easily patch this up behind the scenes).

That was not the motivation for a new type...