E0582 - Error codes index
Description: Book listing all Rust error codes

# Error code E0582

A lifetime is only present in an associated-type binding, and not in the input types to the trait.

Erroneous code example:

    fn bar<F>(t: F)
        // No type can satisfy this requirement, since `'a` does not
        // appear in any of the input types (here, `i32`):
        where F: for<'a> Fn(i32) -> Option<&'a i32>
    {
    }

    fn main() { }

To fix this issue, either use the lifetime in the inputs, or use `'static`. Example:

    fn bar<F, G>(t: F, u: G)
        where F: for<'a> Fn(&'a i32) -> Option<&'a i32>,
              G: Fn(i32) -> Option<&'static i32>,
    {
    }

    fn main() { }

This error also includes the use of associated types with lifetime parameters.

    #![allow(unused)]
    fn main() {
    trait Foo {
        type Assoc<'a>;
    }

    struct Bar<X, F>
    where
        X: Foo,
        F: for<'a> Fn(X::Assoc<'a>) -> &'a i32
    {
        x: X,
        f: F
    }
    }

The latter scenario encounters this error because `Foo::Assoc<'a>` could be implemented by a type that does not use the `'a` parameter, so there is no guarantee that `X::Assoc<'a>` actually uses `'a`.

To fix this we can pass a dummy parameter:

    #![allow(unused)]
    fn main() {
    trait Foo {
        type Assoc<'a>;
    }
    struct Bar<X, F>
    where
        X: Foo,
        F: for<'a> Fn(X::Assoc<'a>, /* dummy */ &'a ()) -> &'a i32
    {
        x: X,
        f: F
    }
    }

Note: The examples above used to be (erroneously) accepted by the compiler, but this was since corrected. See issue #33685 for more details.