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The trait object Foo+Copy implements the trait Copy #32963
Description
select considers the trait object type Foo+Copy to implement the trait Copy, and therefore its supertraits Clone and Sized. This is totally bogus, as the trait object type is not Sized.
For example:
use std::{fmt, mem};
fn size_of_copy<T: Copy+?Sized>() -> usize { mem::size_of::<T>() }
fn main() {
println!("{}", size_of_copy::<fmt::Debug+Copy>());
}This obviously should not compile, but it does (and prints 16, because of the size_of unsized hack).
Activity
arielb1 commentedon Apr 14, 2016
cc @nikomatsakis
nikomatsakis commentedon Apr 15, 2016
@arielb1 indeed.
nikomatsakis commentedon Apr 15, 2016
triage: P-high
arielb1 commentedon Apr 16, 2016
I am working on a fix.
Rollup merge of rust-lang#33039 - bluss:trait-obj-error, r=arielb1
nikomatsakis commentedon Apr 18, 2016
@arielb1 saw your ping on IRC; it seems like we simply should consider
Copyto be object-unsafe. Ideally with a warning period.nikomatsakis commentedon Apr 18, 2016
(I've always thought that unsized types would be move-only.)
Auto merge of #33138 - arielb1:sized-shortcut, r=nikomatsakis