Confusion about impls without for

[gkoz]

Can we use `impl Trait` and `impl Trait for Trait`?

Trait identifiers are slightly overloaded: they've got their normal thing (impl Trait for ..., T: Trait etc.), but they are also the name of the trait object type that allows for erasing a type and performing virtual dispatch of the trait's method. So, these uses are just impl Type/impl Trait for Type using the trait name to refer to that trait object type, rather than the trait itself. E.g. trait Trait {} impl Trait { fn method(&self) {} } creates a inherent method called method on the tr…