Thanks for the prompt reply!

On Tue, 11 Jul 2023 at 12:53, Jonathan Wakely <cxx@kayari.org> wrote:

Why should Thingy3() = default; give you that behaviour? It's still trivial and it is noexcept. Why should it prevent Thingy3() from zeroing the members?

The phrasing of this question assumes zeroing the members is some natural default and deviating from it requires justification. I believe in C++ it's the other way around: you don't pay for what you don't use, so me & quite a few people I talked to would expect `= default` to consistently not initialize the members, in all initialization forms.

One could just as well ask: "Why should `=default` prevent `Thingy3 t3;` from zeroing the members?" - except that it does, and it is very natural to expect consistent impact of `=default`.

If defining it as defaulted behaved how you want, then there would be no way to say "it's default constructible, but I still want it to be trivial". If you do want it to be non-trivial, you can already do that, as you did for Thingy2.

Not sure I understand this, and if I do - not sure I agree. If you want to say "it's default constructible, but the ctor zeros members" (is that what you mean by 'trivial'?) then there certainly is a way to express it: just write a default ctor that zeros the members.