Why Ruby array[array.length, count] returns []?

Question

Possible Duplicate:
Is there some kind of unseen Array termination in Ruby?
Array slicing in Ruby: looking for explanation for illogical behaviour (taken from Rubykoans.com)

a = %w[a b c]
a[3, 1]    # => []
a[4, 1]    # => nil

Could anyone explain why a[3, 1] returns []? Why not nil instead?

Thank you.

You mean `array[array.index, array.length]`? Your title is a bit confusing. — lemoncider, Sep 23 '11 at 05:16
@lemoncider Yes, the title is a bit confusing, but I just want to specify that the **array.index** equals to **array.length**. — Sambath Prum, Sep 23 '11 at 05:27

score 3 · Answer 1 · answered Sep 23 '11 at 05:19

Well, looks like Ruby core documentation only mark this as "special case". According to The Ruby Programming Language(O'Reilly,2008), the comment on this case is:

a[arr_len, len] #=> [], empty array right at the end
a[arr_len + 1, len] #=> nil, nonthing beyond that

No further explanation is given. So I think you should just remember the "special case".

Why Ruby array[array.length, count] returns []?

1 Answers1