From: Yukihiro Matsumoto <matz@...>
Date: 2007-10-30T16:12:53+09:00
Subject: Re: new Enumerable.butfirst method

Hi,

In message "Re: new Enumerable.butfirst method"
    on Tue, 30 Oct 2007 13:41:39 +0900, David Flanagan <david@davidflanagan.com> writes:

|You wrote in your recent changelog entry:
|
|	* enum.c (enum_butfirst): add a new method to iterates over
|	  elements but first n.  RDoc need to be updated.
|
|I'd be happy to update the rdoc comment, but it looks okay as it is to 
|me.  Did you just want an example added?  Or something else?

I was not confident about my English description.  If it's OK, it's
OK.  Thanks.

|I should say, however, that I don't care for the name 'butfirst'.

It's a traditional name (but slightly different behavior) inherited
from Logo.  In Logo, butfirst is cdr in Lisp, which returns given list
with its first element removed.

|I've got three alternatives to propose:
|
|1) How about 'skip' (or 'discard') instead, which would nicely support 
|its use as an enumerator like this:
|
|     c.skip(n).map {|x|...}  # map all but the first n
|
|If you like this, I'd also propose 'only' (or 'limit'):
|
|     c.only(n).map { |x| ...} # iterates no more than n elements from c

We already have #first, that works in reverse of #butfirst.  I am not
sure skip/only pair is better, especially when #only would work same
as #first.

|2) Another idea would be to be more verbose than 'butfirst': 
|each_but_first, which is much clearer and is similar to the existing 
|each_with_index.  Then the opposite method would be each_but_only to 
|iterate only the first n?

It's redundant, when we want to call #butfirst on Enumerator, e.g.

  (1..1000).map{|x| x*2}.butfirst(2).with_index{|x,i| p [x,i]}

|3) Is there some way to integrate your butfirst with the earlier added 
|take and drop methods?  If you removed the form of drop and take that 
|accept a block, and modified them to be iterators instead of returning 
|an array, then you'd end up with this butfirst, with a much more natural 
|(in my opinion) name.

Hmm, drop (which is new in 1.9) to work as butfirst may be a better
idea than just adding butfirst.  Let me consider.

							matz.