E0212 - Error codes index
Description: Book listing all Rust error codes

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# Error code E0212

Cannot use the associated type of a trait with uninferred generic parameters.

Erroneous code example:

    #![allow(unused)]
    fn main() {
    pub trait Foo<T> {
        type A;

        fn get(&self, t: T) -> Self::A;
    }

    fn foo2<I : for<'x> Foo<&'x isize>>(
        field: I::A) {} // error!
    }

In this example, we have to instantiate `'x`, and we don't know what lifetime to instantiate it with. To fix this, spell out the precise lifetimes involved. Example:

    #![allow(unused)]
    fn main() {
    pub trait Foo<T> {
        type A;

        fn get(&self, t: T) -> Self::A;
    }

    fn foo3<I : for<'x> Foo<&'x isize>>(
        x: <I as Foo<&isize>>::A) {} // ok!

    fn foo4<'a, I : for<'x> Foo<&'x isize>>(
        x: <I as Foo<&'a isize>>::A) {} // ok!
    }