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"Static" methods should not be object safe #19949

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#20325
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"Static" methods should not be object safe#19949
#20325

Description

@nikomatsakis
nikomatsakis
opened on Dec 17, 2014

While reading the object safety code I found this:

ty::StaticExplicitSelfCategory => {
    // Static methods are always object-safe since they
    // can't be called through a trait object
    return msgs
}

I think this is sadly incorrect. The whole idea of object safety is to ensure that an object type Foo implements the trait Foo. But if that is the case, then we can have an example like this one:

trait Foo for Sized? {
    fn make() -> Self; // static method
}

fn use<Sized? F:Foo>() {
    let x = Foo::make();
}

fn main() {
    use::<Foo>();
}

cc @nick29581
cc @aturon

Activity

  1. nikomatsakis commented on Dec 17, 2014

    @nikomatsakis
    nikomatsakis
    on Dec 17, 2014
    ContributorAuthor

    I hope that fixing this doesn't cause another round of annoyed users. :(

  2. ftxqxd commented on Dec 17, 2014

    @ftxqxd
    ftxqxd
    on Dec 17, 2014
    Contributor

    See #18527, the PR that introduced this, and rust-lang/rfcs#428, which is the same issue as this one.

  3. nrc
    added a commit that references this issue on Dec 30, 2014

    Forbid static methods in object safe traits

    cd31e6f
  4. alexcrichton
    added a commit that references this issue on Dec 31, 2014

    rollup merge of rust-lang#20325: nick29581/obj-safety-static

    d058520
  5. bors
    closed this as completedin #20325on Dec 31, 2014
  6. lnicola
    added a commit that references this issue on Jun 9, 2025

    Merge pull request rust-lang#19949 from ChayimFriedman2/stabilize-json

    37c8788
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