How to declare an extension static function in Kotlin on Java Classes?

Question

I want declaring an extension func in kotlin but on Java classes Library, I know that do in Kotlin when you resolve companion in extension function. Like:

class Food {
   companion object {
       fun foo() = Unit
   }
}

fun Food.Companion.clear(){/*Clear all of objects*/}

Now, are there any way for inject a static function on Java classes library?

As far as I understand it's not possible as long as a class have no companion object. Btw there is no "injection" of functions. The compiler transforms your fun A.ext(): B into a static B ext(A receiver) — gpunto
– gpunto, Commented Nov 23, 2019 at 9:30

Rujul Gandhi · Accepted Answer · 2019-11-23 09:33:44Z

5

No you can't do it. That issue is already in tracked, please check this for more information.

answered Nov 23, 2019 at 9:33

Rujul Gandhi

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Comments

Abdur Rahman · Accepted Answer · 2019-11-23 09:13:38Z

-2

Create a class somewhere in project named Extensions.kt. It should be looks like this:

package com.examplle.something

fun Food.clear(){
    /*Clear all of objects*/
}

fun User.xyz(){
    /*Do task XYZ*/
}

No need to make a class for this. It should be out of the class.

So finally we'll have a file Extensions.kt which contains only the extensions method directly without any class structure.

answered Nov 23, 2019 at 9:13

Abdur Rahman

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3 Comments

ImanX Over a year ago

I want to inject a static fun in Java Classes library like Navigation Component that developed by Java

Abdur Rahman Over a year ago

This will work fine with any class. Just replace the Food or User to specific class name that you want to insert a new method in.

Eugen Pechanec Over a year ago

You call it on objects. OP wants to call it on class. Imagine fun Int.increment() = this + 1 being called like 1.increment() not Int.increment().

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