Failing to understand a rust generic function error

Question

I was trying to get a piece of Rust generic code to compile, and after mucking around for while narrowed it down to failure of this code to compile. I am not sure what exactly is breaking down here (E0308 doesn't help me much) -- I must be missing something silly:

fn is_fail<bool>() -> bool { false }
fn main(){
  let failure:bool = is_fail();
  //if ! failure {
    println!("{}", failure);
  //}
}

The error is:

error: mismatched types [--explain E0308]
 --> <anon>:1:30
1 |> fn is_fail<bool>() -> bool { false }
  |>                              ^^^^^ expected type parameter, found bool
note: expected type `bool`
note:    found type `bool`

starblue · Accepted Answer · 2016-07-13T10:12:09.953

2

In your function the type parameter bool shadows the builtin type bool. So your function declaration is essentially the same as

fn is_fail<T>() -> T { false }

which clearly isn't well-typed.

edited Jul 13 '16 at 10:12

answered Jul 12 '16 at 06:04

starblue

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1

Yes, but now it is clear why it is wrong. `false` is not of a generic type `T`. – starblue Jul 12 '16 at 07:09
Yes.. type "bool" is shadowed by type parameter "bool"! – sgldiv Jul 12 '16 at 07:39

Failing to understand a rust generic function error

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