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Document association of generic arguments in path segments #2275
Description
There are some subtle behaviors around where generic arguments can appear in a path, particularly with enum variants. For example:
enum E<T> {
V1 { x: T },
}
fn main() {
// These seem to be the same.
E::V1::<i32> { x: 1 };
E::<i32>::V1 { x: 1 };
}Are these exactly the same? I'm wondering if there are other oddities like this? This came up when looking at rust-lang/rust#154971.
#2165 is adding more documentation on generic arguments and how they are associated, but I don't think it covers this.
Activity
fmease commentedon May 30, 2026
They're meant to be equivalent. Historically speaking,
E::V1::<i32>was the original form andE::<i32>::V1came second (but the details are slightly more messy). Years ago, some people advocated for deprecating one of the two forms but nothing ended up happening.rust-lang/rust#154962 is only one example of a gross bug related to the "
E::<…>::Vform", rust-lang/rust#108224 is another one that I also fixed recently (in rust-lang/rust#154918).