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Methods that return unsized types can be (uselessly) codegened #26376

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#71541
Closed
Methods that return unsized types can be (uselessly) codegened#26376
#71541
Labels
A-codegenArea: Code generationA-type-systemArea: Type systemC-enhancementCategory: An issue proposing an enhancement or a PR with one.E-needs-testCall for participation: An issue has been fixed and does not reproduce, but no test has been added.P-lowLow priorityT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

Description

@arielb1
arielb1
opened on Jun 17, 2015
trait Foo {
    fn foo(&self) -> [u8];
}

fn foo(f: Option<&Foo>) {
    if let Some(f) = f {
        let _ = f.foo();
    }
}

fn main() { foo(None) }

This does generate code that calls foo in the vtable, but is not particularly useful.

cc @nikomatsakis

Activity

  1. steveklabnik
    added
    A-type-systemArea: Type system
    on Jun 23, 2015
  2. brson
    added
    A-codegenArea: Code generation
    P-lowLow priority
    on Jan 12, 2017

  3. brson commented on Jan 12, 2017

    @brson
    brson
    on Jan 12, 2017
    Contributor

    Still a problem?

  4. nikomatsakis commented on Jan 12, 2017

    @nikomatsakis
    nikomatsakis
    on Jan 12, 2017
    Contributor

    It's still true, but I'm not especially worried about it.

  5. Mark-Simulacrum
    added
    C-enhancementCategory: An issue proposing an enhancement or a PR with one.
    I-compiletimeIssue: Problems and improvements with respect to compile times.
    on Jul 22, 2017

  6. durka commented on Aug 29, 2018

    @durka
    durka
    on Aug 29, 2018
    Contributor

    Isn't it a bug that you can declare such a trait at all? There's no way to implement it, right?

  7. jonas-schievink
    added
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    on Jan 31, 2020

  8. jonas-schievink commented on Jan 31, 2020

    @jonas-schievink
    jonas-schievink
    on Jan 31, 2020
    Contributor

    This code is now rejected with:

    error[E0161]: cannot move a value of type [u8]: the size of [u8] cannot be statically determined
 --> src/main.rs:7:17
  |
7 |         let _ = f.foo();
  |                 ^^^^^^^

error: aborting due to previous error
  9. jonas-schievink
    added
    E-needs-testCall for participation: An issue has been fixed and does not reproduce, but no test has been added.
    and removed
    I-compiletimeIssue: Problems and improvements with respect to compile times.
    on Jan 31, 2020
  10. Dylan-DPC-zz
    added a commit that references this issue on Apr 25, 2020

    Rollup merge of rust-lang#71541 - wesleywiser:issue_26376, r=Dylan-DPC

    fde4727
  11. bors
    added a commit that references this issue on Apr 26, 2020

    Auto merge of rust-lang#71566 - Dylan-DPC:rollup-9xoz6fg, r=Dylan-DPC

    b592b37
  12. bors
    closed this as completedin fde4727on Apr 26, 2020
  13. fmease
    added
    A-type-systemArea: Type system
    and removed
    A-type-systemArea: Type system
    on Dec 21, 2024
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    A-codegenArea: Code generationA-type-systemArea: Type systemC-enhancementCategory: An issue proposing an enhancement or a PR with one.E-needs-testCall for participation: An issue has been fixed and does not reproduce, but no test has been added.P-lowLow priorityT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

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