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Your example is misleading. If Foo is a trait Box<Foo> and Box<dyn Foo> are the same thing. Impl Foo is for static dispatch. Illustrating the need to dump the

• weavie 8y ago
  Ah ok, I'm back to being confused again then! Is this right: If Foo is a struct then Box<Foo> is static dispatch. If Foo is a trait Box<dyn Foo> is dynamic dispatch, but then so is Box<Foo> - but that is the regrettable point. So from now on, if Foo is a trait we should be writing Box<dyn Foo>, which is largely syntactic sugar to make the situation more clear? I don't fully understand what the release notes are saying about using impl Trait. When would you use Box<impl Foo> vs Box<dyn Foo>?
  • steveklabnik 8y ago
    You are right. It’s not that you would use Box<impl Foo>, but when taking about the two features, it’s easier to compare them, as they’re actually distinct syntactically.
    • weavie 8y ago
      Thankyou.