From: Robert <bob.news@...>
Date: 2003-05-30T21:08:29+09:00
Subject: Re: Iteration - last detection

Detecting if the first element might in some circumstances server the same
purpose and it's easy done without Thread tricks:

def print_format(enum)
  first = true
  str = "["

  enum.each do |e|
    if first
      first = false
    else
      str << ", "
    end

    str << e.to_s
  end

  str << "]"
  str
end


a=[10, 30, "foo"]
puts print_format(a)

    robert


"Carlos" <angus@quovadis.com.ar> schrieb im Newsbeitrag
news:20030530113250.GB1403@quovadis.com.ar...
> > Is there any built in functionality for iteration that will allow me to
> > detect when I am on the last element?  This would not be hard for an
Array,
> > using array.length, but what about a Hash?  How would I know when I am
at
> > the last element?
>
> Here is a module that implements it, but you should include it in every
> class where you want #each to behave that way :-/. (And some #each-like
> methods (for example, String#each_byte, don't work at all...)
>
> oe.rb:
> #!/usr/bin/ruby
>
> class Object
> def last?
> Thread.current.last_iteration?
> end
> private :last?
> end
>
> class Thread
> def last_iteration?
> @__last_iteration__
> end
> end
>
> module EachWithLast
> def EachWithLast.append_features(klass)
> old_each="each_"+rand(10000).to_s+Time.now.usec.to_s
> klass.class_eval <<-FINISH
> alias_method :#{old_each}, :each
>
> def each(*a,&b)
> element = nil
> flag = false
> #{old_each}(*a) { |e|
> Thread.current.instance_eval {
> @__last_iteration__=false
> }
> b.call element if flag
> flag=true
> element=e
> }
> if flag
> Thread.current.instance_eval {
> @__last_iteration__=true
> }
> b.call element
> Thread.current.instance_eval {
> @__last_iteration__=false
> }
> end
> end
> FINISH
> end
> end
>
> class Array; include EachWithLast end
>
> a = [1,2,3,4,5].select {|e| last? }
> p a  # => [5]
>
> class Range; include EachWithLast end
> class String; include EachWithLast end
>
> for i in 1..10
> print "and the last is: " if last?
> print i
> "ds\njkd\njsk\nsd".each { |l| puts " - the last line is #{l}" if last? }
> end
>
> class File; include EachWithLast end
> File.open("oe.rb") { |f|
> count = 0
> f.each { |line|
> count += line.length
> print "last line: #{line}" if last?
> }
> print "total chars: #{count}\n"
> }
> #THE LAST LINE
>