At the basic level, there’s not much difference, but they’re still there. Haskell describes functions or values defined in a typeclass as ‘methods’, just as traits describe OOP methods in the objects they enclose. However, Haskell deals with these differently, treating them as individual values rather than pinning them to an object as OOP would … Read more
A sealed trait can be extended only in the same file as its declaration. They are often used to provide an alternative to enums. Since they can be only extended in a single file, the compiler knows every possible subtypes and can reason about it. For instance with the declaration: sealed trait Answer case object … Read more
Public Service Announcement: I want to state for the record that I believe traits are almost always a code smell and should be avoided in favor of composition. It’s my opinion that single inheritance is frequently abused to the point of being an anti-pattern and multiple inheritance only compounds this problem. You’ll be much better … Read more
I can think of two differences Abstract classes can have constructor parameters as well as type parameters. Traits can have only type parameters. There was some discussion that in future even traits can have constructor parameters Abstract classes are fully interoperable with Java. You can call them from Java code without any wrappers. Traits are … Read more
It is predominately used for Dependency Injection, such as in the Cake Pattern. There exists a great article covering many different forms of dependency injection in Scala, including the Cake Pattern. If you Google “Cake Pattern and Scala”, you’ll get many links, including presentations and videos. For now, here is a link to another question. … Read more
Your last one was almost there: trait A { function calc($v) { return $v+1; } } class MyClass { use A { calc as protected traitcalc; } function calc($v) { $v++; return $this->traitcalc($v); } } The trait is not a class. You can’t access its members directly. It’s basically just automated copy and paste…