From: Brian Candler <B.Candler@...>
Date: 2005-07-13T17:47:43+09:00
Subject: Re: accessing index inside map

On Wed, Jul 13, 2005 at 01:46:17AM +0900, nobu.nokada@softhome.net wrote:
> > However, perhaps 'to_enum' could be called something friendlier, e.g.
> > 
> >   obj.using(:each_with_index).inject(0) {|sum,(a,i)| sum + a*i}
> 
> `using' sounds too general.
> 
> > In fact, even
> > 
> >   obj.enum(:each_with_index).inject(0) {|sum,(a,i)| sum + a*i}
> > 
> > reads better to me, as it's not stressing the creation of an intermediate
> > object. to_foo looks like you are converting obj into something completely
> > different, rather than just adding a temporary wrapper.
> 
> Enumerable#to_enum has an alias named as #enum_for.

The preposition "for" doesn't really sound right here. I don't think we are
enumerating "for" each_with_index; we are enumerating "with"
each_with_index, or "using", or perhaps "over".

The underscore also seems to break up the line visually. Now I know the full
details, I can understand the following, but there are two visual breaks
between the 'map' and the object being enumerated over:

    obj.enum_for(:each_with_index).map { .. }
            ^                     ^
          break                 break

I think that

    obj.enum(:each_with_index).map { .. }

is more clearly a single method call separating the object and its map.

The idea of an enumeration method returning an Enumerator if called without
a block is interesting:

    obj.each_with_index.map { .. }

although this means that every enumeration method you write needs extra code
to support this behaviour. And I dread to think what happens if you start to
chain these methods :-)

This mechanism requires every programmer to do more work in their
enumeration methods. In that case, I still prefer to modify every method in
Enumerable instead: i.e.

    obj.map(:each_with_index) { .. }

But only one person has commented on this so far.

Regards,

Brian.