Benefits of using `Hash#fetch` over `Hash#[]`

Question

I am not sure in what situation I would want to use Hash#fetch over Hash#[]. Is there a common scenario in where it would be of good use?

Answer 1

However, you can do this:

arr = [1,2,3]
arr[1..-2] #=> [1,2]

But not this:

arr.fetch(1..-2) #=> TypeError: no implicit conversion of Range into Integer

Similarly you can mutate an array with Hash#[]

arr[0] = "A"
arr #=> ["A",2,3]

But not with fetch:

arr.fetch(0) = "A" #=> unexpected '=', expecting end-of-input