# Error code E0220

The associated type used was not defined in the trait.

Erroneous code example:

ⓘ

    trait T1 {
        type Bar;
    }

    type Foo = T1<F=i32>; // error: associated type `F` not found for `T1`

    // or:

    trait T2 {
        type Bar;

        // error: Baz is used but not declared
        fn return_bool(&self, _: &Self::Bar, _: &Self::Baz) -> bool;
    }

Run

Make sure that you have defined the associated type in the trait body. Also, verify that you used the right trait or you didn’t misspell the associated type name. Example:

    trait T1 {
        type Bar;
    }

    type Foo = T1<Bar=i32>; // ok!

    // or:

    trait T2 {
        type Bar;
        type Baz; // we declare `Baz` in our trait.

        // and now we can use it here:
        fn return_bool(&self, _: &Self::Bar, _: &Self::Baz) -> bool;
    }

Run

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