CODEWITHSUNDEEP
rust
Ibraheem Ahmed
Ibraheem Ahmed

Reputation: 13518

Why are nested associated type paths considered ambiguous?

Why are nested associated type paths considered ambiguous?

fn flatten<I>(iter: I) -> Option<I::Item::Item>
where
    I: Iterator,
    I::Item: IntoIterator,
{
    None
}

error[E0223]: ambiguous associated type
 --> src/lib.rs:1:34
  |
1 | fn flatten<I>(iter: I) -> Option<I::Item::Item>
  |                                  ^^^^^^^^^^^^^ help: use fully-qualified syntax: `<<I as Iterator>::Item as Trait>::Item`

Shouldn't the compiler be able to resolve the path without fully-qualified syntax? There is only one type I could be referring to, so I don't see why it is ambiguous. Is this a limitation of the compiler or is it intended behavior?

Upvotes: 11

Views: 612

Answers (1)

Shepmaster
Shepmaster

Reputation: 430671

This is a compiler limitation: Nested associated type projection is overly conservative #38078. There's a bit of hope that chalk will improve the situation, but there's no guarantee that it will.

Upvotes: 11

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