traits

I have a struct that mostly encapsulates a vector: struct Group<S> { elements: Vec<S> } I also have a simple trait which is also implemented for other structs: trait Solid { fn intersect(&self, ray: f32) -> f32; } I want to implement Solid for Group , but I want to be able to use Group both for lists of the same implementation of Solid and for lists of mixed implementations of Solid . Basically I want to use both Group<Box<Solid>> and Group<Sphere> ( Sphere implements Solid ). Currently I am using something like this: impl Solid for Group<Box<Solid>> { fn intersect(&self, ray: f32) -> f32 { /

I see that traits in Scala are similar to interfaces in Java (but interfaces in Java extend other interfaces, they don't extend a class). I saw an example on SO about traits usage where a trait extends a class. What is the purpose of this? Why can traits extend classes? adelbertc 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 with

I have a trait Foo pub trait Foo { fn do_something(&self) -> f64; } and a struct which references that trait pub struct Bar { foo: Foo, } Trying to compile I get error: reference to trait `Foo` where a type is expected; try `Box<Foo>` or `&Foo` Changing the struct to struct Bar { foo: &Foo, } Tells me error: missing lifetime specifier Changing the definition to struct Bar { foo: Box<Foo>, } Compiles — yay! However, when I want a function to return foo on bar - something like: impl Bar { fn get_foo(&self) -> Foo { self.foo } } Well obviously bar.foo is a Box<Foo> , so expectedly I get error:

What is the difference between Mixins and Traits? According to Wikipedia , Ruby Modules are sort of like traits. How so? 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 composing class (=class using the traits) ad 2. There may be the name conflict. Two mixins ( MA and MB ) or traits ( TA and TB ) define method with the same