[]Keyword Self

The implementing type within a trait or impl block, or the current type within a type definition.

Within a type definition:

struct Node {
    elem: i32,
    // `Self` is a `Node` here.
    next: Option<Box<Self>>,
}
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In an impl block:

struct Foo(i32);

impl Foo {
    fn new() -> Self {
        Self(0)
    }
}

assert_eq!(Foo::new().0, Foo(0).0);
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Generic parameters are implicit with Self:

struct Wrap<T> {
    elem: T,
}

impl<T> Wrap<T> {
    fn new(elem: T) -> Self {
        Self { elem }
    }
}
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In a trait definition and related impl block:

trait Example {
    fn example() -> Self;
}

struct Foo(i32);

impl Example for Foo {
    fn example() -> Self {
        Self(42)
    }
}

assert_eq!(Foo::example().0, Foo(42).0);
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