traits

I'd like to use the stackable trait pattern with singleton objects, but i can't seem to find how to make the compiler happy: abstract class Pr { def pr() } trait PrePostPr extends Pr { abstract override def pr() { println("prepr") super.pr() println("postpr") } } object Foo extends Pr with PrePostPr { def pr() = println("Foo") } Trying to evaluate this in the repl produces the following error: <console>:10: error: overriding method pr in trait PrePostPr of type ()Unit; method pr needs `override' modifier def pr() = println("Foo") It can, but like this: abstract class Pr { def pr() } trait

I have a trait Foo . I want to force implementors to define a method, if those implementors implement another trait ( Clone in this example). My idea ( Playground ): trait Foo { // Note: in my real application, the trait has other methods as well, // so I can't simply add `Clone` as super trait fn foo(&self) where Self: Clone; } struct NoClone; impl Foo for NoClone {} Sadly, this leads to: error[E0046]: not all trait items implemented, missing: `foo` --> src/lib.rs:8:1 | 2 | / fn foo(&self) 3 | | where 4 | | Self: Clone; | |____________________- `foo` from trait ... 8 | impl Foo for NoClone {}

I have this class Zgh\FEBundle\Entity\User which extends FOS\UserBundle\Model\User . use FOS\UserBundle\Model\User as BaseUser; class User extends BaseUser implements ParticipantInterface { use BasicInfo; // .. } And BaseUser class: abstract class User implements UserInterface, GroupableInterface { protected $id; // .. } And BaseInfo trait: trait BasicInfo { /** * @ORM\Column(type="string", length=255) * @ORM\Id * @ORM\GeneratedValue(strategy="NONE") */ protected $id; // .. } But when I run my code i get this error: Strict standards: FOS\UserBundle\Model\User and Zgh\FEBundle\Model\Partial

Consider the code below: trait A { def work = { "x" } } trait B { def work = { 1 } } class C extends A with B { override def work = super[A].work } Class C won't compile in scala 2.10, because of "overriding method work in trait A of type => String; method work has incompatible type". How to choose one specific method? I'm afraid there is no way to do that. The super[A].work way works only if A and B have the same return types. Consider this: class D extends B .... val test: List[B] = List(new C(), new D()) test.map(b => b.work) //oops - C returns a String, D returns an Int Scala simply

In Java: public interface Foo { public static final int Bar = 0; } And in Scala, how can I create a trait Foo that has Bar , and I can access it as: Foo.Bar ? You can create a companion object (to make it the equivalent of static) and define the variable there using the final val keywords (to make it the equivalent of a final constant): trait Foo { } object Foo { final val Bar = 0 } Lots more on this here 来源： https://stackoverflow.com/questions/8867316/scala-trait-is-there-an-equivalent-of-java-interface-public-static-field