On Mon, Feb 28, 2022 at 12:14:44PM -0800, Linus Torvalds wrote: > On Mon, Feb 28, 2022 at 12:10 PM Linus Torvalds > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > We can do > > > > typeof(pos) pos > > > > in the 'for ()' loop, and never use __iter at all. > > > > That means that inside the for-loop, we use a _different_ 'pos' than outside. > > The thing that makes me throw up in my mouth a bit is that in that > > typeof(pos) pos > > the first 'pos' (that we use for just the typeof) is that outer-level > 'pos', IOW it's a *different* 'pos' than the second 'pos' in that same > declaration that declares the inner level shadowing new 'pos' > variable. The new "pos" has not yet been declared, so this has to refer to the outer "pos", it cannot be the inner one. Because it hasn't been declared yet :-) Compare this to typeof (pos) pos = pos; where that last "pos" *does* refer to the newly declared one: that declaration has already been done! (So this code is UB btw, 6.3.2.1/2). > If I was a compiler person, I would say "Linus, that thing is too ugly > to live", and I would hate it. I'm just hoping that even compiler > people say "that's *so* ugly it's almost beautiful". It is perfectly well-defined. Well, it would be good if we (GCC) would document it does work, and if someone tested it on LLVM as well. But it is really hard to implement it to *not* work :-) > Because it does seem to work. It's not pretty, but hey, it's not like > our headers are really ever be winning any beauty contests... It is very pretty! Needs a comment though :-) Segher
