C++26's Delete with a reason

[lefticus]

I think this syntax maybe should be been reserved for a conditional delete?

https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2573r2.html#alt-syntax

[LB--]

Thankfully we already have conditional = delete using requires clauses, so all we lost was making the syntax more terse.

[lefticus]

Coming in Ep 471