Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.ruby > #3150

Re: anonymous closures with Proc,new, lambda and ->

Show key headers only | View raw

Brian Candler wrote in post #993704:
> And you can do the same without explicitly binding 'counter_maker'
> either:
>
> c = lambda { |init| lambda { init += 1 } }.call(200)
> c.call  # 201
> c.call  # 202

Which of course simplifies to:

c = lambda { init = 200; lambda { init += 1 } }.call
c.call  # 201
c.call  # 202

The outer lambda here is just to ensure that 'init' is in its own scope, 
so if you run this code multiple times, each lambda returned has an 
independent instance of 'init'

Note: this only works as long as 'init' hasn't already been seen 
outside; if it has, all the lambdas will bind to the same 'init'.

In ruby 1.9 there's a way to force it to be local:

c = lambda { |;init| init = 200; ...etc... }.call

But in that case the original code would be shorter:

c = lambda { |init| ...etc... }.call(200)

This does the same in 1.9 (because block parameters are always local), 
but in 1.8 it would still bind to the outside 'init' variable if one 
exists.

-- 
Posted via http://www.ruby-forum.com/.

Back to comp.lang.ruby | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

anonymous closures with Proc,new, lambda and -> Stu <stu@rubyprogrammer.net> - 2011-04-19 01:07 -0500
  Re: anonymous closures with Proc,new, lambda and -> Robert Klemme <shortcutter@googlemail.com> - 2011-04-19 02:30 -0500
  Re: anonymous closures with Proc,new, lambda and -> Brian Candler <b.candler@pobox.com> - 2011-04-19 03:05 -0500
    Re: anonymous closures with Proc,new, lambda and -> Brian Candler <b.candler@pobox.com> - 2011-04-19 03:15 -0500
      Re: anonymous closures with Proc,new, lambda and -> Stu <stu@rubyprogrammer.net> - 2011-04-19 04:57 -0500
        Re: anonymous closures with Proc,new, lambda and -> Brian Candler <b.candler@pobox.com> - 2011-04-19 07:24 -0500
          Re: anonymous closures with Proc,new, lambda and -> Adam Prescott <adam@aprescott.com> - 2011-04-19 14:55 -0500
      Re: anonymous closures with Proc,new, lambda and -> Stu <stu@rubyprogrammer.net> - 2011-04-19 16:43 -0500
        Re: anonymous closures with Proc,new, lambda and -> 7stud -- <bbxx789_05ss@yahoo.com> - 2011-04-19 18:48 -0500
        Re: anonymous closures with Proc,new, lambda and -> 7stud -- <bbxx789_05ss@yahoo.com> - 2011-04-19 21:28 -0500
          Re: anonymous closures with Proc,new, lambda and -> Stu <stu@rubyprogrammer.net> - 2011-04-20 01:03 -0500
            Re: anonymous closures with Proc,new, lambda and -> Robert Klemme <shortcutter@googlemail.com> - 2011-04-20 02:23 -0500
              Re: anonymous closures with Proc,new, lambda and -> Steve Klabnik <steve@steveklabnik.com> - 2011-04-20 05:55 -0500
            Re: anonymous closures with Proc,new, lambda and -> 7stud -- <bbxx789_05ss@yahoo.com> - 2011-04-20 12:32 -0500
              Re: anonymous closures with Proc,new, lambda and -> Steve Klabnik <steve@steveklabnik.com> - 2011-04-20 12:59 -0500
                Re: anonymous closures with Proc,new, lambda and -> Brian Candler <b.candler@pobox.com> - 2011-04-20 15:40 -0500
                Re: anonymous closures with Proc,new, lambda and -> 7stud -- <bbxx789_05ss@yahoo.com> - 2011-04-20 19:51 -0500
                Re: anonymous closures with Proc,new, lambda and -> Stu <stu@rubyprogrammer.net> - 2011-04-21 01:31 -0500
                Re: anonymous closures with Proc,new, lambda and -> Brian Candler <b.candler@pobox.com> - 2011-04-21 04:34 -0500
                Re: anonymous closures with Proc,new, lambda and -> Robert Klemme <shortcutter@googlemail.com> - 2011-04-21 06:13 -0500
                Re: anonymous closures with Proc,new, lambda and -> Robert Klemme <shortcutter@googlemail.com> - 2011-04-21 09:20 -0500
                Re: anonymous closures with Proc,new, lambda and -> 7stud -- <bbxx789_05ss@yahoo.com> - 2011-04-21 11:56 -0500
                Re: anonymous closures with Proc,new, lambda and -> Steve Klabnik <steve@steveklabnik.com> - 2011-04-21 12:06 -0500
                Re: anonymous closures with Proc,new, lambda and -> Robert Klemme <shortcutter@googlemail.com> - 2011-04-27 06:49 -0500
                Re: anonymous closures with Proc,new, lambda and -> Stu <stu@rubyprogrammer.net> - 2011-04-27 13:33 -0500
                Re: anonymous closures with Proc,new, lambda and -> Steve Klabnik <steve@steveklabnik.com> - 2011-04-27 17:06 -0500
  Re: anonymous closures with Proc,new, lambda and -> 7stud -- <bbxx789_05ss@yahoo.com> - 2011-04-19 13:02 -0500
    Re: anonymous closures with Proc,new, lambda and -> Brian Candler <b.candler@pobox.com> - 2011-04-19 13:19 -0500
      Re: anonymous closures with Proc,new, lambda and -> Steve Klabnik <steve@steveklabnik.com> - 2011-04-19 13:26 -0500
        Re: anonymous closures with Proc,new, lambda and -> Michael Edgar <adgar@carboni.ca> - 2011-04-19 13:51 -0500
          Re: anonymous closures with Proc,new, lambda and -> Brian Candler <b.candler@pobox.com> - 2011-04-20 10:18 -0500
            Re: anonymous closures with Proc,new, lambda and -> Jeremy Bopp <jeremy@bopp.net> - 2011-04-20 12:44 -0500

csiph-web