Android Development with Kotlin

The withIndex and indexed variants

Sometimes, the element processing method depends on its index in the list. The most universal way to solve this problem is by using the withIndex function, which returns a list of values with indexes:

    listOf(9,8,7,6).withIndex() // 1 
       .filter { (i, _) -> i % 2 == 0 } // 2 
       .forEach { (i, v) -> print("$v at $i,") }  
    // Prints: 9 at 0, 7 at 2, 

1. The withIndex function packs each element into IndexedValue, which contains both the elements and its index.

2. In a lambda, IndexedValue is deconstructed into index and value, but while the value is unused, an underscore is placed instead. It might be omitted, but this code is more readable. This line only filters elements with an even index.

Also, there are variants ...