From: Patrick Hurley <phurley@...>
Date: 2005-03-31T04:51:06+09:00
Subject: Re: Syntax sugar idea for loops

On Thu, 31 Mar 2005 04:37:42 +0900, Eric Hodel <drbrain@segment7.net> wrote:
> On 30 Mar 2005, at 11:23, Berger, Daniel wrote:
> 
> >> From: pmak@aaanime.net [mailto:pmak@aaanime.net]
> >>
> >> Consider the following Ruby code:
> >>
> >>     every_other = true
> >>     people.each do |person|
> >>         every_other = !every_other
> >>         row_class = every_other ? 'row1' : 'row2'
> >>         puts "<tr class=#{row_class}><td>#{person.name}</td>
> >> <td>#{person.email}</td></tr>"
> >>     end
> >>
> >> Consider these two lines of the code, though:
> >>
> >>     every_other = true
> >>         every_other = !every_other
> >>
> >> These lines could be replaced by syntax sugar. Traction has
> >> the following "Special Loop Tags":
> >>
> >>     <loop.first>: true if this is the first iteration of the loop
> >>     <loop.inner> true if this is not the first or last
> >> iteration of the loop
> >>     <loop.odd> true if this is an odd iteration
> >>     <loop.last>: true if this is the last iteration of the loop
> >
> > I think Enumerable#each_with_index largely eliminates the need for such
> > syntactic sugar.  Consider:
> >
> > people.each_with_index do |person, i|
> >    puts "First person: #{person}" if i == 0
> >    row_class = i%2 == 0 ? "row1" : "row2"
> >    puts "<tr class=#{row_class}><td>#{person.name}</td>
> >    puts "Last person: #{person}" if i == people.length - 1
> > end
> >
> > I suppose you could extend Fixnum within a loop to include extra
> > methods
> > so that you could do something like this:
> 
> people.each_with_index do |person, i|
>     puts "First person: #{person} if person == people.first
>     row_class = i.even? ? "row1" : "row2"
>     puts "Last person: #{person} if person == people.last
> end
> 
> How about that?
> 
> --
> Eric Hodel - drbrain@segment7.net - http://segment7.net
> FEC2 57F1 D465 EB15 5D6E  7C11 332A 551C 796C 9F04
> 
> 

And you could of course do something like (hey is this a valid use for
@@vars or is there a better way? -- does Ruby have the C concept of a
local static variable?)

class Object
  @@nasty_bad_pseudo_global_hash = Hash.new(true)
  def alternate(*args)
    doit = @@nasty_bad_pseudo_global_hash[caller.first]
    @@nasty_bad_pseudo_global_hash[caller.first] = !doit
    yield(args) if doit
  end
end

(1..10).each do |i|
  alternate(i) { |x| puts x }
end