CODEWITHSUNDEEP
rust
krixon
krixon

Reputation: 195

Why don't Option's Some and None variants need to be qualified?

According to the docs for Option, Option is an enum with variants Some<T> and None.

Why is it possible to refer to Some and None without qualifying them?

For example, this works fine:

let x = Option::Some(5);
match x {
    Some(a) => println!("Got {}", a),
    None => println!("Got None"),
}

But this fails to compile:

enum Foo<T> {
    Bar(T),
    Baz,
}
let x = Foo::Bar(5);
match x {
    Bar(a) => println!("Got {}", a),
    Baz => println!("Got Baz"),
}

The error from the compiler is unresolved enum variant, struct or const `Bar`

Upvotes: 16

Views: 2135

Answers (1)

Levans
Levans

Reputation: 15002

The Rust prelude, which is automatically inserted into every source file, contains this line:

pub use option::Option::{self, Some, None};

Which brings Option and both its variants in scope.

Upvotes: 25

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