Regression in integer fallback

[SiegeLord]

This code compiled fine before 1.0.0-nightly (4be79d6 2015-01-23 16:08:14 +0000):

fn main()
{
    for i in 0..100
    {
        i as f32;
    }
}

But with that version, it now gives this error:

<anon>:5:3: 5:11 error: the type of this value must be known in this context
<anon>:5        i as f32;
                ^~~~~~~~

[ghost]

changing 0 to 0u32 should work, I stumbled upon the same thing and the doc seems to be updated: http://doc.rust-lang.org/book/looping.html (see at the very bottom)

EDIT: Maybe worth noting that these work:

    for x in 0..10 {
        println!("{}", x);                                                       
    }

    for x in range(0, 10) {
        println!("{}", x);
    }

    for i in range(0,100)
    {
      i as f32;
    }

[SiegeLord]

That's just a workaround to a bug (not sure if that was implied). i should fall back to being i32 as per the existence of the integer fallback.

[nikomatsakis]

I don't necessarily expect this to work. Fallback comes late in the process, once all constraints are known, but as (like method dispatch) requires the type being cast to be known immediately.

[nikomatsakis]

It's plausible we could make it work since we know that the type is integral (I imagine that's how it ever worked, not sure what would have changed that, though it might have been something I did). It occurs to me though that this is somewhat forward-hostile to the idea of integer literals ever being used for anything other than plain ints (but enabling such a feature may well wind up requiring opt-in anyway).

[nikomatsakis]

(Though really it's sort of silly that as requires the type to be known immediately, so I guess fixing that would be another way to ease the forward compat fears.)

[ghost]

I thought this was a feature because it's saying that it doesn't know if it's u32 or i32 for example. Would it assume it's unsigned only if it contains negative numbers in the range?
EDIT3: what @SiegeLord said makes sense: https://github.com/rust-lang/rfcs/blob/master/text/0212-restore-int-fallback.md

---

EDIT2: ignore the following, my bad
But I might be missing something because this doesn't output anything from for:
EDIT: just realized -1u32 is too big 4294967295 so the following makes sense:

fn main() {
  for i in -1u32..3 {
    if i % 2 == 0 {
      print!("*");
    }
    print!("{}",i);
  }
  println!("");
}

$ rustc main.rs && ./main 
main.rs:2:12: 2:17 warning: negation of unsigned int literal may be unintentional, #[warn(unsigned_negation)] on by default
main.rs:2   for i in -1u32..3 {
                     ^~~~~

There's no output from for, unless using -1i32