Understanding and Resolving Rust Error E0326

Rust Error E0326

Rust Error E0326 occurs when an implementation of a trait doesn't match the type constraint. In other words, the types of any associated constants in a trait implementation must match the types in the trait definition.

Erroneous code example:

#![allow(unused)]
fn main() {
trait Foo {
    const BAR: bool;
}

struct Bar;

impl Foo for Bar {
    const BAR: u32 = 5; // error, expected bool, found u32
}
}

In the above code, the compiler would generate an Error E0326 because the type of the associated constant 'BAR' in the trait implementation does not match the type of 'BAR' in the trait definition.

Fixing the Error E0326

In order to fix Error E0326, you have to ensure that the types of any associated constants in a trait implementation match the types in the trait definition. To accomplish that, you can do the following:

1. Review the trait definition and identify the correct type of the associated constant.

2. Modify the trait implementation to use the correct type for the associated constant.

In our previous erroneous code example, we can now provide a correct implementation by changing the type of 'BAR' in the trait implementation from 'u32' to 'bool'.

The corrected code would look like this:

#![allow(unused)]
fn main() {
trait Foo {
    const BAR: bool;
}

struct Bar;

impl Foo for Bar {
    const BAR: bool = true;
}
}

Now the implementation of the trait 'Foo' for the struct 'Bar' has a matching type for the associated constant 'BAR', and the Error E0326 is resolved.