go - Keyed items in golang array initialization

Question

In a pub quiz by Dave Cheney I came across the following construct:

a := [...]int{5, 4: 1, 0, 2: 3, 2, 1: 4}
fmt.Println(a)

>> [5 4 3 2 1 0]

(Playground Link)

It seems you can use keys in the initialization fields of an array (4: 1, 0 means set element at index 4 to 1, element at index 5 to 0). I have never seen something like this before. What is its use case? Why not set the particular index directly?

Answer 1

Waitting for answers