"Multiple applicate methods in scope" error on unambiguous method call

[japaric]

STR

trait FooChar {
    fn foo(&self, char) {}
}

trait FooInt {
    fn foo(&self, int) {}
}

impl FooChar for char {}
impl FooInt for char {}

trait Bar<T> {
    fn bar(&self, T) {}
}

impl Bar<char> for char {}
impl Bar<int> for char {}

fn main() {
    'a'.foo('b');  //~ error: multiple applicable methods in scope
    'a'.bar('b');  // OK
}

Output

conflict.rs:20:9: 20:17 error: multiple applicable methods in scope [E0034]
conflict.rs:20     'a'.foo('b');  //~ error: multiple applicable methods in scope
                       ^~~~~~~~
conflict.rs:2:5: 2:24 note: candidate #1 is defined in the trait `FooChar`
conflict.rs:2     fn foo(&self, char) {}
                  ^~~~~~~~~~~~~~~~~~~
conflict.rs:6:5: 6:23 note: candidate #2 is defined in the trait `FooInt`
conflict.rs:6     fn foo(&self, int) {}
                  ^~~~~~~~~~~~~~~~~~
error: aborting due to previous error

Version

rustc 0.13.0-dev (98958bcaf 2014-11-05 10:21:38 +0000)

---

I'm under the impression that 'a'.foo('b') should just work, although there are two traits that provide the foo method, it's clear from the signature of the method call that FooChar should be used. After all, it's possible to do something similar using multidispatch (the Bar trait)

cc @nikomatsakis

[nikomatsakis]

I don't think this is expected to work. The way method selection works, it needs to be able to narrow to at least a specific trait, without considering the types of the arguments. In the case of FooChar vs FooInt, we can't narrow to a specific trait based solely on the receiver. (In the case of Bar, we can -- the Bar trait).