On Wed, 21 Jan 2026 at 19:00, Thiago Macieira <thiago@macieira.org> wrote:

On Wednesday, 21 January 2026 09:41:12 Pacific Standard Time Jan Schultke
wrote:
> > > Because the result of std::bit_cast has unspecified padding bits, so x =
> >
> > Unless we change std::bit_cast, which is what I am proposing.
>
> It would be an ABI break if you changed that, and compilers would
> essentially have to invent new ABI for all kinds of platforms to make this
> work, so the std::bit_cast that you're proposing is practically
> unimplementable.

Why are you saying that? How is the behaviour of std::bit_cast ABI in the first
place?

Because it's a function and returns by value, so it's limited by the calling conventions for the platform, and whether those preserve padding (they usually don't). Ergo, at least on a debug build, you're not getting any padding bits from a function call to std::bit_cast.