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Questions tagged [companion-object]

In Scala and Kotlin, an object with the same name as a class, used to hold utility members for the class

In and , a companion object is an object with the same fully qualified name as a class. Companion objects are used to hold utility members that apply to all instances of the class. These can include constants, s (apply), and s. They provide a similar functionality as Java's .

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Avoid duplicate type alias in Scala class and companion object

I'm a newbie in Scala, and I have a Scala program with a class and a companion object, and I want to use a type alias that is used : To define the methods of the class. Also I want to use the alias outside the class. For that I find useful to…
juanrh0011
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Companion Objects of Scala's Traits

I have something like this: trait AO extends A { private var link: String = "AO" //... } trait AR extends A { private var link: String = "AR" //... } object AO extends AO with Atr { atr += link } object AR extends AR with Atr { atr…
Valerin
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How can I guarantee the existence of a method in a companion object and reference it?

Consider this example, where Listable is intended to mixed into the companion object of a case class. Therefore, in order to call Writer.grid, one must have a companion object A that extends Listable[A], with an implicit Writer[A] defined within.…
Michael Zajac
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Access object inside of a companion object in scala

I have the following: case class Location(name: String, level: Location.Level) object Location { trait Level case object City extends Level case object State extends Level } If I try and access City (from another source file), I get an error…
three-cups
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Create companion objects for classes imported from Java

I want to create companion objects for some imported Java types, so that I do not have to use new to allocate them. I want to start with the type Vector3f is imported from com.jme3.math from jMonkeyEngine. What I tried is: package…
Suma
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When is an implicit imported from a companion object?

I know this is the umpteenth implicits / companion object question. However, I did not find this case anywhere yet. In "Tryout", why does A need no import for the implicit class, while B does need it? Thankx. class LongConsumer { def consume(l:…
Georg
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Scala equivalent of static final using a companion object

How could I convert the following into scala. public class JedisDB { private static final JedisPool jedisPool = new JedisPool(getJedisPoolConfig()); public static JedisPoolConfig getJedisPool() { // .. } public int getTest123() { …
Blankman
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Override toString method is not getting called from Companion Object

I thought I can call methods of class once I created the object of that class through companion object. But I am not able to do that. Below is my code: class Employee(val id: Int, val initialBalance: Int) { val message = println("Object created…
Sudipta Deb
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Encapsulating related fields into a companion object/class and avoiding duplication

My application uses a properties-file to load several properties. Every instance of the application has 3 environment-related parameters - one of them is a property, the other two are computed based on it. class Environment(val properties:…
teo
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Companion Object in a List bound by the Related class' super-trait

I am trying put together a "registry" of Companion Objects - by storing them in a List which is bound using Generics. An example is best: trait Foo case class A() extends Foo object A case class B() extends Foo object B case class C() extends…
Ramon
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How to replace static variables with scala available means in a base class

What I need: trait Base { import scala.math.{Pi=>mPi, cos=>msoc, sin=>msin} static val Pi : Float = mPi.toFloat static def cos(phi : Float) : Float = mcos(phi).toFloat static def sin(phi : Float) : Float = msin(phi).toFloat // ... //…
ayvango
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method name qualification when using a companion object

I am just learning Scala. I created a companion object (see code snippet below) where I define an operator, ^, (to represent complex conjugation). I have to qualify it with the companion objects name inside the associated class. I was under the…
user1641083
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Why fields declaration with var/val not allowed in apply method of companion object

I am using scala 2.12 and IntelliJ IDE. I tried to auto-generate apply method in Scala companion object using readily available template. It generated apply method with fields having val because I have created class having fields declared as val in…
Gunjan Shah
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How to mix in self annotations in companion object

Consider the following situation: trait M { } // uses N object M { def apply = new M { } } trait N { self: L => } trait L { val m: B } type B M needs new trees definitions that are created in N. I don't want to pass around these new trees…
user1868607
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Private value of a Scala class is not accessible in the companion Object

I have a Scala class and it's companion object (in Client.scala) as follows: class Client(val key: Int) { private val num_bits = 5 } object Client { val count_entries = Math.pow(2, num_bits).toInt println(count_entries) } However,…
PankajK
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