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kotlinlang

You can define those fonctions as extensions of the original type, so that you define them once for all classes implementing that type :
`fun &lt;T&gt; Iterable.forEach(action: (T) -&gt; Unit)`

But, why would you write your own implementation of `forEach` ? It is already available as an extension function in the Kotlin stdlib, and not only for Java 8 : 
<https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/for-each.html>