From: Robert Klemme <bob.news@...>
Date: 2005-07-12T18:50:50+09:00
Subject: Re: accessing index inside map

Brian Candler wrote:
> On Tue, Jul 12, 2005 at 10:04:02AM +0100, Brian Candler wrote:
>>   module Enumerable
>>     def altmap(meth=:each)
>>       res = []
>>       send(meth) { |*args| res << yield(*args) }
>>       res
>>     end
>>   end
>
> P.S. I note that some Enumerable methods already take arguments:
> detect/find, grep, inject could have meth=:each as a later argument
> for backwards-compatibility.
>
> The only awkward ones are to_set and zip. Even then, they could be
> made backwards-compatible by checking if the first argument is a
> Symbol and using it as a method name in that case.
>
> I don't really see the usefulness of the foo.to_set(klass,*args)
> syntax anyway, given that it just calls klass.new(foo,*args).
> However, I can see uses for
>     h.to_set(:each_key)
>     h.to_set(:each_value)

IMHO the enumerator approach is slightly superior as your suggestion can
lead to conflicts with current method arguments as you have noticed.
Personally I don't have a problem using

a.to_enum(:each_with_index).inject(0) {|sum,(a,i)| sum + a*i}

I think this is more flexible and modularized.  And the overhead of a new
instance creation is usually neglectible compared to the iteration
overhead.

Kind regards

    robert