This isn’t possible directly now. However, RFC 1210: impl specialization contains various aspects that will make this sort of behaviour work, for example, something like this should work: trait Foo { fn method(&self) { println!(“default implementation”); } } trait Bar: Foo { … } partial impl<T: Bar> Foo for T { default fn method(&self) { … Read more
Can traits be used on enum types? Yes. In fact, you already have multiple traits defined for your enum; the traits Debug, Copy and Clone: #[derive(Debug, Copy, Clone)] pub enum SceneType The problem is that you aren’t attempting to implement Playable for your enum, you are trying to implement it for one of the enum’s … Read more
Yes they can, a trait that extends a class puts a restriction on what classes can extend that trait – namely, all classes that mix-in that trait must extend that class. scala> class Foo defined class Foo scala> trait FooTrait extends Foo defined trait FooTrait scala> val good = new Foo with FooTrait good: Foo … Read more
This is the tricky point of trait objects, you need to be very explicit about who owns the underlying object. Indeed, when you use a trait as a type, the underlying object must be stored somewhere, as trait objects are in fact references to an object implementing the given trait. This is why you cannot … Read more
Mixins may contain state, (traditional) traits don’t. Mixins use “implicit conflict resolution”, traits use “explicit conflict resolution” Mixins depends on linearization, traits are flattened. Lecture about traits ad 1. In mixins you can define instance variables. Traits do not allow this. The state must be provided by the composing class (=class using the traits) ad … Read more
I should be able to implement Rand for AllValues since AllValues is defined in my crate. No, you are only allowed to implement your own trait AllValues for types you didn’t define. You can’t make the logical jump to implementing an unrelated trait that you also didn’t define. There are two considerations to remember: If … Read more
You can get the syntax by using marker interfaces and extension methods. Prerequisite: the interfaces need to define the contract which is later used by the extension method. Basically the interface defines the contract for being able to “implement” a trait; ideally the class where you add the interface should already have all members of … Read more
Can I avoid eager ambiguity resolution for trait implementations with generics? No. Is it possible to have [ambiguity resolution to be done at the call site, rather than at the definition site]? No. There’s a (long-delayed) RFC for specialization that will allow overlapping trait implementations, but only when one of them is more specific than … Read more
It’s a shortcoming of Scala’s type system. When determining the members in a mixin, Scala uses two rules: First, concrete always overrides abstract. Second, If two members are both concrete, or both abstract, then the one that comes later in linearization order wins. Furthermore, the self type of a trait trait S { this: C … Read more
First, some logical errors with the code: It is not correct to cast pointers to i32 on many platforms (like 64-bit). Pointers may use all of those bits. Truncating a pointer and then calling a function at the truncated address will lead to Really Bad Things. Generally you want to use a machine-sized integer (usize … Read more