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Tracking Issue for impl for<'a> Trait<'a> #104288

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@oli-obk

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@oli-obk
Contributor

Some context can be found in this comment.

We would like to support using higher kinded lifetimes in opaque types.

At present

#![feature(type_alias_impl_trait)]

trait Tr<'a> {
    type Assoc;
}

impl<'a> Tr<'a> for () {
    type Assoc = ();
}

type Associated<'a> = impl Copy;
type Associated2<'a> = impl Copy + 'a;

fn f() -> impl for<'a> Tr<'a, Assoc = Associated2<'a>> {}
fn f1() -> impl for<'a> Tr<'a, Assoc = Associated<'a>> {}

impl<'a> Tr<'a> for i32 {
    type Assoc = &'a ();
}

fn f2() -> impl for<'a> Tr<'a, Assoc = Associated2<'a>> { 42_i32 }
fn f3() -> impl for<'a> Tr<'a, Assoc = Associated<'a>> { 42_i32 }

errors, though with a different error message than the equivalent code for RPIT.

An implementation should also add tests that actually use the higher kinded lifetimes, e.g. via closures or similar datastructures.

About tracking issues

Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.

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added
C-tracking-issueCategory: An issue tracking the progress of sth. like the implementation of an RFC
on Nov 11, 2022
SkiFire13

SkiFire13 commented on Nov 13, 2022

@SkiFire13
Contributor

The issue title seems to be swapping the impl and for<'a>

changed the title [-]Tracking Issue for `for<'a> impl Trait<'a>`[/-] [+]Tracking Issue for `impl for<'a> Trait<'a>`[/+] on Nov 21, 2022
added
C-bugCategory: This is a bug.
and removed
C-tracking-issueCategory: An issue tracking the progress of sth. like the implementation of an RFC
on Nov 30, 2022
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    C-bugCategory: This is a bug.F-type_alias_impl_trait`#[feature(type_alias_impl_trait)]`

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          Tracking Issue for `impl for<'a> Trait<'a>` · Issue #104288 · rust-lang/rust