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Questions tagged [traits]

In computer programming, a trait is a collection of methods, used as a "simple conceptual model for structuring object oriented programs"

In computer programming, a trait is a collection of methods, used as a "simple conceptual model for structuring object oriented programs".

Traits have the following properties

  • Provides a set of methods that implement behaviour.
  • Requires a set of methods that parameterize the provided behaviour.
  • Does not specify any state variables.
  • Never directly accesses state variables.

Can be composed

  • Trait composition is symmetric and conflicting methods are excluded from the composition.
  • Can be nested, but the nesting has no semantics for classes.
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Why PHP Trait can't implement interfaces?

I'm wondering why PHP Trait (PHP 5.4) cannot implement interfaces. Update from user1460043's answer => ...cannot require class which uses it to implement a specific interface I understand that it could be obvious, because people could think that if…
Leto
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How do I implement the Add trait for a reference to a struct?

I made a two element Vector struct and I want to overload the + operator. I made all my functions and methods take references, rather than values, and I want the + operator to work the same way. impl Add for Vector { fn add(&self, other:…
Jeremy Sorensen
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How can I dispatch on traits relating two types, where the second type that co-satisfies the trait is uniquely determined by the first?

Say I have a Julia trait that relates to two types: one type is a sort of "base" type that may satisfy a sort of partial trait, and the other is an associated type that is uniquely determined by the base type. (That is, the relation from BaseType ->…
Philip
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What makes something a "trait object"?

Recent Rust changes have made "trait objects" more prominent to me, but I only have a nebulous grasp of what actually makes something into a trait object. One change in particular is the upcoming change to allow trait objects to forward trait…
Shepmaster
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How can I implement Rust's Copy trait?

I am trying to initialise an array of structs in Rust: enum Direction { North, East, South, West, } struct RoadPoint { direction: Direction, index: i32, } // Initialise the array, but failed. let data = [RoadPoint {…
tehnyit
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What are the pros of using traits over abstract classes?

Can someone please explain traits in Scala? What are the advantages of traits over extending an abstract class?
Zack Marrapese
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How to overload class constructor within traits in PHP >= 5.4

In PHP 5, I can to overload constructors (and any others methods). But if I get some code like this: class Base { public function __construct($a, $b) { echo $a+$b; } public function sayHello() { echo 'Hello '; …
Guy Fawkes
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How do I implement a trait I don't own for a type I don't own?

I wanted to implement the Shl trait for Vec, the code is below. This would make things like vec << 4 possible, which would be nice sugar for vec.push(4). use std::ops::Shl; impl Shl for Vec { type Output = Vec; fn shl(&self,…
le_me
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PHP traits - defining generic constants

What is the best way to define constants that may be used by a number of classes within a namespace? I'm trying to avoid too much inheritance, so extending base classes is not an ideal solution, and I'm struggling to find a good solution using…
t j
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Is it possible to use `impl Trait` as a function's return type in a trait definition?

Is it at all possible to define functions inside of traits as having impl Trait return types? I want to create a trait that can be implemented by multiple structs so that the new() functions of all of them returns an object that they can all be…
Ameo
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Why is the `Sized` bound necessary in this trait?

I have a trait with two associated functions: trait WithConstructor: Sized { fn new_with_param(param: usize) -> Self; fn new() -> Self { Self::new_with_param(0) } } Why does the default implementation of the second method…
eulerdisk
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How to clone a struct storing a boxed trait object?

I wrote a program that has the trait Animal and the struct Dog implementing the trait. It also has a struct AnimalHouse storing an animal as a trait object Box. trait Animal { fn speak(&self); } struct Dog { name: String, } impl…
Denis Kreshikhin
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How do traits classes work and what do they do?

I'm reading Scott Meyers' Effective C++. He is talking about traits classes, I understood that I need them to determine the type of the object during compilation time, but I can't understand his explanation about what these classes actually do?…
rookie
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What are the similarities and differences between C++'s concepts and Rust's traits?

In Rust, the main tool for abstraction are traits. In C++, there are two tools for abstractions: abstract classes and templates. To get rid of some of the disadvantages of using templates (e.g. hard to read error messages), C++ introduced concepts…
Lukas Kalbertodt
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Mixing multiple traits in Scala

Quick note: Examples from the tutorial Scala for Java Refugees Part 5: Traits and Types. Suppose I have the traits Student, Worker, Underpaid, and Young. How could I declare a class (not instance), CollegeStudent, with all these traits? Note: I am…
Daniel Ribeiro
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