Self Types in Traits
Last time we learned that a scala trait might extend a class. Well — that might offer up a little confusion when the superclass for any of those mixins references when looking at self references. For this reason, scala has self types.
When a trait starts with this:_Type_ => then it can only be mixed into a subclass of the given _Type_. This is similar to a trait with a supertype, when invocations to super were post-fixed with the supertype in brackets (super[_SuperType_].method).
The self type can also be used to specify a structural type — a type that specifies methods a class has without specifying the class itself. Both will compile:
trait Bar { def bar(x: String) }
trait Foo {
this: Bar =>
def log(y: String) {}
}
trait Foo {
this: { def bar(x: String) } =>
def log(y: String) {}
}