is there a way to do it without extracting their “inner” values every time with pattern matching, and without implementing the Add, Sub, … traits and overloading operators? No, the only way is to implement the traits manually. Rust doesn’t have an equivalent to the Haskell’s GHC extension GeneralizedNewtypeDeriving which allows deriving on wrapper types … Read more
It’s a negative trait implementation for the Send trait as described in RFC 19. As a summary: The Send trait is an auto trait, which means it is automatically implemented for all types that only contain other Send types: unsafe auto trait Send {} (Send is also an unsafe trait, which means it is unsafe … Read more
Let’s decompose it one-by-one. Box Box<T> is a pointer to heap-allocated T. We use it here because trait objects can only exist behind pointers. Trait objects In Box<Fn() + Send + ‘static>, Fn() + Send + ‘static is a trait object type. In future, it will be written Box<dyn (Fn() + Send + ‘static)> to … Read more
Traits are similar to interfaces: Traits are Rust’s sole notion of interface. An interface is meant to document available methods, to have an interface with private methods makes no sense. Correspondingly, in Rust you can’t have different levels of visibility in one trait. If you can see the trait, you can always see all of … Read more
The reason is that the base class method is abstract abstract class IntQueue { def get(): Int def put(x: Int) } If you were to not put abstract on the trait you end up with the explanation you were seeking: trait Doubling extends IntQueue { override def put(x: Int) { super.put(2 * x) } } … Read more
No, there is no trait that provides iter(). However, IntoIterator is implemented on references to some containers. For example, Vec<T>, &Vec<T> and &mut Vec<T> are three separate types that implement IntoIterator, and you’ll notice that they all map to different iterators. In fact, Vec::iter() and Vec::iter_mut() are just convenience methods equivalent to &Vec::into_iter() and &mut … Read more
Rust traits and Java interfaces both address the problem of having multiple possible implementations that adhere to some convention/protocol/interface for interacting with a value/object, without constraining the implementation details as a Java superclass does. They can be used in many of the same situations. However, they are different in many details, mostly meaning that Rust … Read more
I don’t know what your source is for the claim that you should prefer traits over abstract classes in Scala, but there are several reasons not to: Traits complicate Java compatibility. If you have a trait with a companion object, calling methods on the companion object from Java requires bizarre MyType$.MODULE$.myMethod syntax. This isn’t the … Read more
Sure, use decltype: auto var_a = bar(t); decltype(var_a) b; You can add cv-qualifiers and references to decltype specifiers as if it were any other type: const decltype(var_a)* b;