Weird interaction between higher-ranked lifetimes and associated type bounds

foo.rs:

pub trait Foo
where
    for<'a> &'a Self: Bar,
    for<'a> <&'a Self as Bar>::Xyz: Clone {}

pub trait Bar {
    type Xyz;
}

impl Foo for () {}

impl<'a> Bar for &'a () {
    type Xyz = usize;
}

Error from rustc 1.0.0-nightly (30e1f9a1c 2015-03-14) (built 2015-03-15)

foo.rs:12:1: 12:19 error: the trait `for<'a> core::clone::Clone` is not implemented for the type `<&'a () as Bar>::Xyz` [E0277]
foo.rs:12 impl Foo for () {}
          ^~~~~~~~~~~~~~~~~~

Current error



rustc 1.17.0 (56124baa9 2017-04-24)
error[E0277]: the trait bound `for<'a> <&'a () as Bar>::Xyz: std::clone::Clone` is not satisfied
  --> <anon>:10:6
   |
10 | impl Foo for () {}
   |      ^^^ the trait `for<'a> std::clone::Clone` is not implemented for `<&'a () as Bar>::Xyz`
   |
   = help: the following implementations were found:
             <&'a T as std::clone::Clone>
   = note: required by `Foo`

error: aborting due to previous error

Compilation failed.

Triage: no change

Trieage: no change.

This code now compiles since 1.56. On 1.55, the error was:

error[E0277]: the trait bound `for<'a> <&'a () as Bar>::Xyz: Clone` is not satisfied
  --> <source>:10:6
   |
1  | pub trait Foo
   |           --- required by a bound in this
...
4  |     for<'a> <&'a Self as Bar>::Xyz: Clone {}
   |                                     ----- required by this bound in `Foo`
...
10 | impl Foo for () {}
   |      ^^^ the trait `for<'a> Clone` is not implemented for `<&'a () as Bar>::Xyz`
   |
   = help: the following implementations were found:
             <&T as Clone>

Navigation Menu

Repository navigation

Weird interaction between higher-ranked lifetimes and associated type bounds #23481

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Weird interaction between higher-ranked lifetimes and associated type bounds #23481

Description

Activity

brson commented on May 4, 2017

steveklabnik commented on Sep 24, 2018

estebank commented on Nov 5, 2019

estebank commented on Jun 8, 2022

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions