Expected trait `Foo', found trait 'MyFoo'

Question

I haven't found why this won't work or what is the proper way to cast this to get it to pass.

I have a trait in an external crate to be executed by a VM (playground):

trait Foo {}

trait Bar {}

trait OtherFoo: Bar {}

impl Foo for dyn OtherFoo {}

fn use_foo(_: &dyn Foo) {}

fn use_other_foo_as_foo(other_foo: &dyn OtherFoo) {
    use_foo(other_foo)
}

I get

error[E0308]: mismatched types
  --> src/lib.rs:12:13
   |
12 |     use_foo(other_foo)
   |             ^^^^^^^^^ expected trait `Foo`, found trait `OtherFoo`
   |
   = note: expected reference `&dyn Foo`
              found reference `&dyn OtherFoo`

I would figure that since it implements the trait that it would be allowed to be passed in but I realize Rust doesn't go by reference and thus a cast of some kind is needed, but I have no idea how to cast this accordingly.

It says I can't use as as that only applies to primitive casts and I haven't been able to find exactly what I'm looking for.

Please [edit] your question to contain a [mre]. I don't want to have to guess what changes to make to your code in order to get the same error you do. You are using a lot of undefined names: `VMError`, `VM`, `EXIT_INTERRUPT`, etc. that obscure the actual problem. — trent, Apr 17 '20 at 17:06
No, not fixed. The example is still not reproducible, and isn't really minimal. — mcarton, Apr 17 '20 at 17:29
Basically, [this](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=60a6a82f25500878dc0b68c9085d55ef) is what you have. — mcarton, Apr 17 '20 at 17:31
Does [this](https://stackoverflow.com/questions/28632968/why-doesnt-rust-support-trait-object-upcasting) answer your question? — mcarton, Apr 17 '20 at 17:33
more like this. https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=896a917121812dc5fe89dc85b2c90194 Will add to the example above. — Richard John Catalano, Apr 17 '20 at 18:10

Expected trait `Foo', found trait 'MyFoo'

0 Answers0