Comments¶

1. An array in Java is not an Iterable (due to design reasons). There is no super class of array and Iterable either in Java. If you want a method to support both array and Iterable as the parameter, you need to overload it (for both array and Iterable.) It is the same situation in Kotlin as Kotlin is mostly Java.

Fold vs Reduce¶

fold takes an initial value, and the first invocation of the lambda you pass to it will receive that initial value and the first element of the collection as parameters. reduce doesn't take an initial value, but instead starts with the first element of the collection as the accumulator (called sum in the following example).

Construct an element with initial values.

Tips and Traps¶

1. Notice that Iterable.map returns a List instead of an iterator. Since almost all collections in Kotlin eventually inherit from Iterable, the map method of all collections (including HashMap) in Kotlin returns List.

References¶

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-iterable/

Create an Empty List¶

sorted¶

If elements in a List implements the Comparable interface, you can call the method sorted to return a sorted List (in nature order).

Note: Pair in Kotin does not implement the Comparable interface!!!