From: Robert Klemme <bob.news@...>
Date: 2004-07-06T22:32:39+09:00
Subject: Re: Array::index and rindex operator


"David A. Black" <dblack@wobblini.net> schrieb im Newsbeitrag
news:Pine.LNX.4.44.0407060521080.8383-100000@wobblini...
> Hi --
>
> On Tue, 6 Jul 2004, Robert Klemme wrote:
>
> >
> > "Kristof Bastiaensen" <kristof@vleeuwen.org> schrieb im Newsbeitrag
> > news:pan.2004.07.06.10.51.04.229075@vleeuwen.org...
> > > Hi,
> > >
> > > On Tue, 06 Jul 2004 09:42:41 +1000, George Ogata wrote:
> > >
> > > > Sometimes though I wish that #index could take a block (i.e.,
return
> > > > the first index for which the block is true).  Unless I'm
overlooking
> > > > something, there doesn't seem to be a method that does this.  I
don't
> > > > know what others think of the idea, but that would probably go
some
> > > > way towards your goal.
> > >
> > > I think that would be nice.  I would vote for it.
> > > You could do this with enumerator, but it is not so compact:
> > >
> > > require "enumerator"
> > >
> > > a = %w(one two three)
> > > a.enum_for(:each_with_index).find { |s, i| s == "two" }[1]
> > > => 1
> >
> > Another solution:
> >
> > a.inject(0) {|i,s| break i if "two" == s; idx+1}
>
> The problem though (aside from 'idx' for 'i' :-)

Thanks for that correction!

> is that you always
> get a number, even if there's no element found:
>
>   [1,2,3].inject(0) {|i,s| break i if "two" == s; i + 1}
>
>   # => 3

True.  The approach is betters suited to a method implementation:

module Enumerable
  def index_2(obj=nil, &b)
    b = lambda {|x| obj == x} unless b
    inject(0) {|i,el| return i if b.call(el); i+1}
    nil
  end
end

Thx for correcting my sloppyness.

    robert