Suppose I have the following code that I want to make as a re-usable component:
fun <T> MutableList<T>.swap(index1: Int, index2: Int) {
val tmp = this[index1] // 'this' corresponds to the list
this[index1] = this[index2]
this[index2] = tmp
}
and I want to use it anywhere in my app as follows:
val l = mutableListOf(1, 2, 3)
l.swap(0, 2)
Correct me if I'm wrong but I believe that function extension declarations can exist outside of a class. So in an Android app, where would I put this declaration? Or does it even matter? Will the compile just compile the code regardless where the extension is declared and make it re-usable globally or do I have to make it part of a class?
You can create some file, e.g. ListExt.kt anywhere you want (for example in package main_package_name/util/ListExt.kt) and place the extension function there and it will be available in the whole project. So the content of the ListExt.kt file can be:
package main_package_name.util
fun <T> MutableList<T>.swap(index1: Int, index2: Int) {
val tmp = this[index1] // 'this' corresponds to the list
this[index1] = this[index2]
this[index2] = tmp
}
// other extension functions on the Lists
They can be anywhere, but it seems to make sense to have extensions for a particular class in the same file and/or package. For example, extensions to String could be in StringExtensions.kt, and that could optionally be in an extensions package.
For a extension to be global, you need to put it outside of class
package com.extension.globalcontext
fun <T> MutableList<T>.swap(index1: Int, index2: Int)
And to call them you need to import the package
import com.extension.globalcontext
l.swap(0, 2)