Trait Method Conflicts

What happens when you have a name conflict between two different trait methods implemented for the same type?

// Copyright 2025 Google LLC
// SPDX-License-Identifier: Apache-2.0

mod ext {
    pub trait Ext1 {
        fn is_palindrome(&self) -> bool;
    }

    pub trait Ext2 {
        fn is_palindrome(&self) -> bool;
    }

    impl Ext1 for str {
        fn is_palindrome(&self) -> bool {
            self.chars().eq(self.chars().rev())
        }
    }

    impl Ext2 for str {
        fn is_palindrome(&self) -> bool {
            self.chars().eq(self.chars().rev())
        }
    }
}

pub use ext::{Ext1, Ext2};

// Which method is invoked?
// The one from `Ext1`? Or the one from `Ext2`?
fn main() {
    assert!("dad".is_palindrome());
}

The trait you are extending may, in a newer version, add a new trait method with the same name as your extension method. Or another extension trait for the same type may define a method with a name that conflicts with your own extension method.

Ask: what will happen in the example above? Will there be a compiler error? Will one of the two methods be given higher priority? Which one?
The compiler rejects the code because it cannot determine which method to invoke. Neither Ext1 nor Ext2 has a higher priority than the other.

To resolve this conflict, you must specify which trait you want to use.

Demonstrate: call Ext1::is_palindrome("dad") or Ext2::is_palindrome("dad") instead of "dad".is_palindrome().

For methods with more complex signatures, you may need to use a more explicit fully-qualified syntax.
Demonstrate: replace "dad".is_palindrome() with <str as Ext1>::is_palindrome("dad") or <str as Ext2>::is_palindrome("dad").

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Trait Method Conflicts