The really short version is simpler because you can’t. That’s not how Traits work. When you write use SomeTrait; in PHP you are (effectively) telling the compiler to copy and paste the code from the Trait into the class where it’s being used. Because the use SomeTrait; is inside the class, it can’t add implements … Read more
A class can only extend one superclass, and thus, only one abstract class. If you want to compose several classes the Scala way is to use mixin class composition: you combine an (optional) superclass, your own member definitions and one or more traits. A trait is restricted in comparison to classes in that it cannot … Read more
Yes, there is. You just have to define new trait like this: trait MySoftDeletes { use SoftDeletes { SoftDeletes::saveWithHistory as parentSaveWithHistory; } public function saveWithHistory() { $this->parentSaveWithHistory(); //your implementation } }
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
There are two ways to do downcasting in Rust. The first is to use Any. Note that this only allows you to downcast to the exact, original concrete type. Like so: use std::any::Any; trait A { fn as_any(&self) -> &dyn Any; } struct B; impl A for B { fn as_any(&self) -> &dyn Any { … Read more
A def can be implemented by either of a def, a val, a lazy val or an object. So it’s the most abstract form of defining a member. Since traits are usually abstract interfaces, saying you want a val is saying how the implementation should do. If you ask for a val, an implementing class … Read more
The short answer is: it’s safe if you use them safely 🙂 The snarky answer: tell me what you mean by traits, and maybe I’ll give you a better answer 🙂 In all seriousness, the term “trait” is not well-defined. Many Java developers are most familiar with traits as they are expressed in Scala, but … Read more
Funny, I’ve just written a function_traits implementation based on Specializing a template on a lambda in C++0x which can give the parameter types. The trick, as described in the answer in that question, is to use the decltype of the lambda’s operator(). template <typename T> struct function_traits : public function_traits<decltype(&T::operator())> {}; // For generic types, … Read more
I guess one would have to look into languages that have Traits for some time now to learn the accepted Good/Best practices. My current opinion on Trait is that you should only use them for code that you would have to duplicate in other classes that share the same functionality. Example for a Logger trait: … 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