Mediocre error message for f32/f64 ambiguity

[nieksand]

I have this code:

    let _ = |x: f64| x * 2.0.exp();

https://play.rust-lang.org/?gist=58e23173aec4b798d8021af0ead25bbd&version=nightly

I get this error message:

error[E0599]: no method named `exp` found for type `{float}` in the current scope

I can work around by:

    let _ = |x: f64| x * 2.0f64.exp();

The world would be a better place if:

• Type inference could just figure out 2.0 has to be f64 given the type on x
• Failing that, an error message indicating the problem is f32 vs f64 ambiguity rather than this mysterious {float} thing

[kennytm]

Note that type inference cannot figure out 2.0 is an f64 just by x * 2.0.exp() because this is perfectly valid.

struct Foo;
trait Wat {
    fn exp(self) -> Foo;
}
impl Wat for f32 {
    fn exp(self) -> Foo { Foo }
}
impl std::ops::Mul<Foo> for f64 {
    type Output = &'static str;
    fn mul(self, _: Foo) -> &'static str {
        "wat"
    }
}

fn main() {
    let _ = |x: f64| x * 2.0.exp();
    //let _ = |x: f64| x * 2.0f64.exp();
}

[nieksand]

Yipes. Inference is definitely out.