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Function type with opaque return type can be coerced to `dyn Fn` with arbitrary...

 2 years ago
source link: https://github.com/rust-lang/rust/issues/98608
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Nilstrieb commented 22 days ago •

edited

I tried this code:

fn hi() -> impl Sized { std::ptr::null::<u8>() }

fn main() {
    let b: Box<dyn Fn() -> Box<u8>> = Box::new(hi);
    let boxed = b();
    let null = *boxed;
    println!("{null:?}");
}

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=a78a1c65a7788a1fc16bbb49823e31b1

I expected to see this happen: Compiler error, since impl Sized cannot be coerced to Box<u8>.

Instead, this happened: Code compiles, segfault

rustc --version --verbose:

rustc 1.64.0-nightly (2f3ddd9f5 2022-06-27)
binary: rustc
commit-hash: 2f3ddd9f594adf9773547aa7cedb43c4ac8ffd2f
commit-date: 2022-06-27
host: x86_64-unknown-linux-gnu
release: 1.64.0-nightly
LLVM version: 14.0.6
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