On Wed, 21 Jan 2026 at 19:00, Thiago Macieira <thiago_at_[hidden]> 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.