Rust error E0411: cannot find type `Self` in this scope

What it meansThe Self keyword was used outside an impl, trait, or type definition.

What rustc prints

error[E0411]: cannot find type `Self` in this scope
 --> main.rs:3:2
  |
2 | fn main() {
  |    ---- `Self` not allowed in a function
3 | <Self>::foo; // error: use of `Self` outside of an impl, trait, or type
  |  ^^^^ `Self` is only available in impls, traits, and type definitions

Real output of rustc 1.99.0 compiling the official example below (2021 edition). Your names and line numbers will differ; the first line is the part to match.

E0411Types and traits

Activein rustc 1.99.0

8related errors linked below

The compiler team's explanation

The Self keyword was used outside an impl, trait, or type definition.

Erroneous code example:

<Self>::foo; // error: use of `Self` outside of an impl, trait, or type
             // definition

The Self keyword represents the current type, which explains why it can only be used inside an impl, trait, or type definition. It gives access to the associated items of a type:

trait Foo {
    type Bar;
}

trait Baz : Foo {
    fn bar() -> Self::Bar; // like this
}

However, be careful when two types have a common associated type:

trait Foo {
    type Bar;
}

trait Foo2 {
    type Bar;
}

trait Baz : Foo + Foo2 {
    fn bar() -> Self::Bar;
    // error: ambiguous associated type `Bar` in bounds of `Self`
}

This problem can be solved by specifying from which trait we want to use the Bar type:

trait Foo {
    type Bar;
}

trait Foo2 {
    type Bar;
}

trait Baz : Foo + Foo2 {
    fn bar() -> <Self as Foo>::Bar; // ok!
}

From rustc --explain E0411 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.

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Often hit nextE0308: mismatched typesA related error from the same family.Read it next →

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Rust error E0411: cannot find type `Self` in this scope

What rustc prints

The compiler team's explanation

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