f32 seen as ambiguous associated type

[pfalabella]

see http://stackoverflow.com/questions/31208465/pi-constant-is-ambiguous

   fn main() {
        let _ = f32::consts::PI;
    }

fails to compile with:

$ rustc -
<anon>:2:13: 2:28 error: ambiguous associated type; specify the type using the syntax `<f32 as Trait>::consts` [E0223]
<anon>:2     let i = f32::consts::PI;
                     ^~~~~~~~~~~~~~~
error: aborting due to previous error

on rust 1.0 stable and 1.1 stable

using the full path std::f32::consts::PI; works. The compilation error looks wrong (why is f32 an associated type)?

[jonas-schievink]

You're using the type f32, not the module, so rustc tries to resolve consts as an associated type. If you put a use std::f32 somewhere, it works.

[pfalabella]

Yes, I probably haven't made myself very clear in the description above.
I've noted that fully specifying the path works, but I still think "ambiguous associated type" referring to f32 is a confusing error message (I can't blame the person asking the SO question for interpreting it as "f32 is an associated type and defined in two or more traits" none of which is true).

[jonas-schievink]

That's true. The message should read something like "no associated type consts found" (at least this seems to be the case here). It would also help if rustc would output a list of implemented Traits that have the ambiguous associated type whenever this happens.

[bluss]

Rustc is underlining all of f32::consts::PI, and it should call it an associated item, not just type.

[steveklabnik]

Triage, with the new errors:

error[E0223]: ambiguous associated type
 --> <anon>:2:17
  |
2 |         let _ = f32::consts::PI;
  |                 ^^^^^^^^^^^^^^^ ambiguous associated type
  |
  = note: specify the type using the syntax `<f32 as Trait>::consts`

ouch 😦

[Mark-Simulacrum]

The consts in the number type modules should probably be moved to associated constants. I believe we're mostly on board with this, but there's not currently an issue to my knowledge.

[abique]

I'm running into this error, this is quite ridiculous to have so much troubles just to use PI.

[agrif]

I ran into this today. I was reading the docs for f32 and all the examples use f32::consts::PI, so color me surprised when attempting to use that results in an associated type error (???).

Of course, the examples also use std::f32; at the top, but that's a pretty dang non-local effect and not something you are looking for right away, and of course the error doesn't point you in anywhere near that direction.

It would probably be best if there were not two different things named f32 here, but I suppose that ship has sailed.

[eminence]

At a minimum, the ambiguous associated type, specify the type using the syntax <f32 as Trait>::consts error message is totally bogus and should be improved