What are the differences between these Array methods

Question

These static Array methods have me puzzled. They seem to do the same things. Are they available for older legacy code?

Array.IndexOf
Array.FindIndex

Array.LastIndexOf
Array.FindLastIndex

Answer 1

FindIndex takes a predicate.

Two different ways to find 6 in:

var nums = new[]{1,3,7,6,5};

First even:

Array.FindIndex(nums, val=>val % 2 == 0);

Value:

Array.IndexOf(nums, 6);

Answer 2

One accepts an item to match. The other other accepts a function that checks an item and return true if matches, false if it does not.

For example:

var x = {1,2,3,4,5,6};
int i = Array.IndexOf(x, 2);
int j = Array.FindIndex(x, a => a == 2);