In match - Rust (rust-lang.org), there is "None::<usize>", what's that mean? Thanks!
let opt = Option::None::<usize>;
let x = match opt {
Some(int) => int,
None => 10,
};
assert_eq!(x, 10);
In match - Rust (rust-lang.org), there is "None::<usize>", what's that mean? Thanks!
let opt = Option::None::<usize>;
let x = match opt {
Some(int) => int,
None => 10,
};
assert_eq!(x, 10);
It's the same as let opt: Option<usize> = None;
The syntax is called turbofish. You can read about it more here
In addition to what @zynaxsoft wrote, one thing I like about turbofish syntax is that it, at least to me, somewhat more clearly illustrates that a None
, when used with an Option<T>
, is tied to the T
. I.e. there isn't a single None
, it's always a part of another type. (This is useful to know because one sometimes ends up in a situation where the compiler tells you it doesn't know what None
is meant, and one needs to annotate it with the specific type).
It means the same thing as <Option<usize>>::None
, but is how the type can be explicitly specified when the variant has already been imported.
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