layer8 on Rust Any part 3: we have upcasts

Comment on Rust Any part 3: we have upcasts parent

Okay, but doesn't Bar nevertheless inherit Foo's methods in the sense of interface inheritance? Or does code that gets passed a Bar not get access to Foo's methods?

the_mitsuhiko 1y

does code that gets passed a Bar not get access to Foo's methods

Prior to the current version of Rust it was impossible to access methods on `Foo` when a `&dyn Bar` was passed. With the current beta version you can upcast.

ogoffart 1y

Prior to the current version of Rust it was impossible to access methods on `Foo` when a `&dyn Bar` was passed.

This has been working since Rust 1.0, I think:

    trait Foo {
        fn foo(&self);
    }
    trait Bar : Foo {}

    impl Foo for () {
        fn foo(&self) { println!("Hello") }
    }
    impl Bar for () {}

    fn xxx(x: &dyn Bar) {
       x.foo();
    }

    pub fn main() {
        xxx(&());
    }

> With the current beta version you can upcast

Right. Now you can convert from `&dyn Bar` to `&dyn Foo` which wasn't possible before.

the_mitsuhiko 1y

Inherent method implementations were unavailable. (Eg: impl dyn Foo) and then call this via Bar.

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