There are two sets of checks happening here, which is why the difference appears confusing. Each type in the function signature is checked for validity. Option inherently requires T: Sized. A return type that doesn’t require Sized is fine: trait Works { fn foo() -> Box<Self>; } The existing answer covers this well. Any function … Read more
You can use num or num-traits crates and bound your generic function type with num::Float, num::Integer or whatever relevant trait: use num::Float; // 0.2.1 fn main() { let f1: f32 = 2.0; let f2: f64 = 3.0; let i1: i32 = 3; println!(“{:?}”, sqrt(f1)); println!(“{:?}”, sqrt(f2)); println!(“{:?}”, sqrt(i1)); // error } fn sqrt<T: Float>(input: T) … Read more
Can traits be used on enum types? Yes. In fact, you already have multiple traits defined for your enum; the traits Debug, Copy and Clone: #[derive(Debug, Copy, Clone)] pub enum SceneType The problem is that you aren’t attempting to implement Playable for your enum, you are trying to implement it for one of the enum’s … Read more
I don’t see how you can possibly do better than struct city { string name; int zipcode; }; There’s nothing non-essential there. You need the types of the two members, your whole question is predicated around giving names to the two members, and you want it to be a unique type. You do know about … Read more
Pointers into an array can be used as random access iterators. There needs to be some consistent way to get these types both for pointers (which obviously can’t have the types declared as nested types, since only classes can have nested types) and for class-type iterators. The traits class template provides this consistent way. The … Read more
This can be done with macros (that are officially a part of Scala since 2.10.0-M3). Here’s a gist example of what you are looking for. 1) My macro generates a local class that inherits from the provided case class and Persisted, much like new T with Persisted would do. Then it caches its argument (to … Read more
The problem with the Application trait is actually described in its documentation: (1) Threaded code that references the object will block until static initialization is complete. However, because the entire execution of an object extending Application takes place during static initialization, concurrent code will always deadlock if it must synchronize with the enclosing object. This … Read more