Why does array.slice behave differently for (length, n)

Question

If I have an array a:

1. a[a.length] returns nil. Good.
2. a[a.length, x] returns []. Good.

Answer 1

To begin with, this case is a special case in Ruby.

This special case also has an explanation to it:

There is a point of difference when you speak about indexing an array, and slicing it.

Indexing an array means to have an unique Position which helps you access the value at a given Index.

Slicing on the other hand means to "cut" between two points (P.S points here are index)

Consider this:

array = [Ruby, PHP, JS, HTML, CSS]

Indexing in this case will be:

array = [Ruby, PHP, JS, HTML, CSS]
Index =   0.    1.  2.  3.    4. 

Slicing in the same case will be:

array = [Ruby, PHP, JS, HTML, CSS]
Slice = 0.   1.   2.  3.    4.   5.

Hence:

array[5,n] #[] i.e. you get an empty array.
array[6,n] #nil i.e. NIL

Reference