# Proc.new and return **URL:** \ **Category:** ruby-talk\ **Created:** [28 February 2008 12:53 UTC](https://rubytalk.org/t/proc-new-and-return/44832 "2008-02-28T12:53:45Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Arlen\_Christian\_Mar1](https://avatars.discourse-cdn.com/v4/letter/a/9de053/32.png) [@Arlen\_Christian\_Mar1](https://rubytalk.org/u/Arlen_Christian_Mar1)\ **Post date:** [28 February 2008 12:53 UTC](https://rubytalk.org/t/proc-new-and-return/44832/1 "2008-02-28T12:53:45Z")
Since it isn't a function! ☹ Now, it can return sometimes -- if it's in a function defition. And you can see that it could come in handy: def slow\_include arr, el   arr.each do |e|     return true if e == el   end   false end p slow\_include([1, 2, 3], 3) p slow\_include([1, 2, 3], 4) Result: true false (of course, you can just use [1, 2, 3].include?(3), but this is for demo) So, the block there returns from the function, like you'd expect. It's up to the controlling function (Array#each in this case) to select a return value. For instance: [2, 4, 6].map {|q| return q \* 2} What's the expected output? Do we simply get "4" as the entire evaluation? Remember that Array#map itself is supposed to return a value (the array with values mapped!). So, blocks can't really return anything - it makes no sense. HTH, Arlen > **···** > > On Thu, Feb 28, 2008 at 11:39 PM, S2 \ wrote: > > > I am sure this is a really easy question for most of you, but i was not > > able to find an answer to this, or to understand the difference between > > this two: > > > > $ irb > > irb(main):001:0\> a = Proc.new {true} > > =\> #\ > > irb(main):002:0\> b = a.call > > =\> true > > irb(main):003:0\> a = Proc.new {return true} > > =\> #\ > > irb(main):004:0\> b = a.call > > LocalJumpError: unexpected return > >         from (irb):3 > >         from (irb):4:in `call' > >         from (irb):4 > >         from :0 > > > > why can't a block return something? ---
**Author:** ![Arlen\_Christian\_Mar1](https://avatars.discourse-cdn.com/v4/letter/a/9de053/32.png) [@Arlen\_Christian\_Mar1](https://rubytalk.org/u/Arlen_Christian_Mar1)\ **Post date:** [28 February 2008 13:19 UTC](https://rubytalk.org/t/proc-new-and-return/44832/2 "2008-02-28T13:19:42Z")
Excellent. 🙂 Glad we could help. [I speak too on Jari's behalf here, it seems. I'm sure he's glad too. :)] Arlen > **···** > > On Fri, Feb 29, 2008 at 12:15 AM, S2 \ wrote: > > > with your post and that of Jari i now understand: > > > > irb(main):001:0\> [2, 4, 6].map {|q| return q \* 2} > > LocalJumpError: unexpected return > >         from (irb):1 > >         from (irb):1:in `map' > >         from (irb):1 > > > > as expected. but if i put it inside a method > > > > irb(main):002:0\> def hello > > irb(main):003:1\> [2, 4, 6].map {|q| return q \* 2} > > irb(main):004:1\> end > > =\> nil > > irb(main):005:0\> hello > > =\> 4 ---
**Author:** ![ThoML](https://avatars.discourse-cdn.com/v4/letter/t/d78d45/32.png) [@ThoML](https://rubytalk.org/u/ThoML)\ **Post date:** [28 February 2008 13:19 UTC](https://rubytalk.org/t/proc-new-and-return/44832/3 "2008-02-28T13:19:58Z")
> as expected. but if i put it inside a method AFAIK the way return inside a block works has changed in ruby 1.9 though (it then returns from the block). ---
**Author:** ![Sebastian\_Hungereck1](https://avatars.discourse-cdn.com/v4/letter/s/3ab097/32.png) [@Sebastian\_Hungereck1](https://rubytalk.org/u/Sebastian_Hungereck1)\ **Post date:** [28 February 2008 15:33 UTC](https://rubytalk.org/t/proc-new-and-return/44832/4 "2008-02-28T15:33:39Z")
Arlen Cuss wrote: > Remember that Array#map itself is supposed to return a value (the array > with values mapped!). So, blocks can't really return anything - it makes no > sense. Blocks return the value of the last expression in them (or, if you break from the block, they return the value given to break, the same way return works for methods). What the yielding method does with that return value depends, as you say, on the method, but you can't say that blocks don't return anything. HTH, Sebastian > **···** > > -- > Jabber: sepp2k@jabber.org > ICQ: 205544826 ---
**Author:** ![Arlen\_Christian\_Mar1](https://avatars.discourse-cdn.com/v4/letter/a/9de053/32.png) [@Arlen\_Christian\_Mar1](https://rubytalk.org/u/Arlen_Christian_Mar1)\ **Post date:** [28 February 2008 13:29 UTC](https://rubytalk.org/t/proc-new-and-return/44832/5 "2008-02-28T13:29:07Z")
Hi, > \> as expected. but if i put it inside a method > > AFAIK the way return inside a block works has changed in ruby 1.9 > though (it then returns from the block). Hmm... I don't see this behaviour, but I may be out of date. irb(main):004:0\> RUBY\_VERSION =\> "1.9.0" irb(main):005:0\> Proc.new {return true}.call LocalJumpError: unexpected return         from (irb):5:in `block (3 levels) in irb\_binding'         from (irb):5:in `call'         from (irb):5         from /usr/lib/ruby/1.9/irb.rb:150:in `block (2 levels) in eval\_input'         from /usr/lib/ruby/1.9/irb.rb:259:in `signal\_status'         from /usr/lib/ruby/1.9/irb.rb:147:in `block in eval\_input'         from /usr/lib/ruby/1.9/irb.rb:146:in `eval\_input'         from /usr/lib/ruby/1.9/irb.rb:70:in `block in start'         from /usr/lib/ruby/1.9/irb.rb:69:in `catch'         from /usr/lib/ruby/1.9/irb.rb:69:in `start'         from /usr/bin/irb1.9:13:in `\' irb(main):006:0\> I can't find any relevant documentation that says it should be otherwise. Arlen. > **···** > > On Fri, Feb 29, 2008 at 12:19 AM, ThoML \ wrote: ---
**Author:** ![Mark\_Bush](https://avatars.discourse-cdn.com/v4/letter/m/e274bd/32.png) [@Mark\_Bush](https://rubytalk.org/u/Mark_Bush)\ **Post date:** [28 February 2008 13:33 UTC](https://rubytalk.org/t/proc-new-and-return/44832/6 "2008-02-28T13:33:47Z")
ThoML wrote: > AFAIK the way return inside a block works has changed in ruby 1.9 > though (it then returns from the block). Not in my copy: irb(main):003:0\> a = Proc.new {return true} =\> #\ irb(main):004:0\> a.call LocalJumpError: unexpected return   from (irb):3:in `block (4 levels) in irb\_binding'   from (irb):4:in `call'   from (irb):4   from /Users/bush/Src/Ruby/Ruby1.9/lib/ruby/1.9.0/irb.rb:149:in `block (2 levels) in eval\_input'   from /Users/bush/Src/Ruby/Ruby1.9/lib/ruby/1.9.0/irb.rb:262:in `signal\_status'   from /Users/bush/Src/Ruby/Ruby1.9/lib/ruby/1.9.0/irb.rb:146:in `block in eval\_input'   from /Users/bush/Src/Ruby/Ruby1.9/lib/ruby/1.9.0/irb.rb:145:in `eval\_input'   from /Users/bush/Src/Ruby/Ruby1.9/lib/ruby/1.9.0/irb.rb:69:in `block in start'   from /Users/bush/Src/Ruby/Ruby1.9/lib/ruby/1.9.0/irb.rb:68:in `catch'   from /Users/bush/Src/Ruby/Ruby1.9/lib/ruby/1.9.0/irb.rb:68:in `start'   from ../Ruby1.9/bin/irb:12:in `\' ruby 1.9.0 (2008-02-21 revision 15557) [i686-darwin9.1.0] > **···** > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![ThoML](https://avatars.discourse-cdn.com/v4/letter/t/d78d45/32.png) [@ThoML](https://rubytalk.org/u/ThoML)\ **Post date:** [28 February 2008 14:50 UTC](https://rubytalk.org/t/proc-new-and-return/44832/7 "2008-02-28T14:50:15Z")
> so in 1.9 > Proc.new { true } > and > Proc.new { return true } > are the same? Okay, it seems I mixed something up here. I think what I actually referred to (I have to admit this currently is as unclear as it is to you) probably is the change that proc has undergone.     def foo(y)         x = lambda {|x| return x}         x.call(y)         return y \* 2     end     def bar(y)         x = proc {|x| return x}         x.call(y)         return y \* 2     end     p [foo(1), bar(1)] With ruby19 you get [2, 1]. With ruby18 it's [2, 2]. ---
**Author:** ![Arlen\_Christian\_Mar1](https://avatars.discourse-cdn.com/v4/letter/a/9de053/32.png) [@Arlen\_Christian\_Mar1](https://rubytalk.org/u/Arlen_Christian_Mar1)\ **Post date:** [28 February 2008 23:44 UTC](https://rubytalk.org/t/proc-new-and-return/44832/8 "2008-02-28T23:44:36Z")
Hi, > Blocks return the value of the last expression in them (or, if you break from > the block, they return the value given to break, the same way return works > for methods). What the yielding method does with that return value depends, > as you say, on the method, but you can't say that blocks don't return > anything. Yes, you're right - I guess what I was trying to say is that you can't have some `return n' or `break n' and \*always\* expect the return value (of the expression including the block) will be `n' - it'll be interpreted by the the actual function that takes the block first (or in the case of return, break out of the function). > > def some\_case > >   a = yield \* 2 > >   a + 5 > > end =\> nil > > some\_case {break 32} =\> 32 > > some\_case {32} =\> 69 > > It's kinda a moot/uninteresting point I'm taking now, though. However, it was new news to meet the semantics of `proc' differed from Proc.new so radically! Thanks guys. Arlen > **···** > > On Fri, Feb 29, 2008 at 2:33 AM, Sebastian Hungerecker \ wrote: ---
**Author:** ![ts1](https://avatars.discourse-cdn.com/v4/letter/t/a8b319/32.png) [@ts1](https://rubytalk.org/u/ts1)\ **Post date:** [28 February 2008 15:04 UTC](https://rubytalk.org/t/proc-new-and-return/44832/9 "2008-02-28T15:04:44Z")
> With ruby19 you get [2, 1]. With ruby18 it's [2, 2]. In 1.9 'proc {}' is the same than 'Proc.new {}', this was not the case with 1.8.6 Guy Decoux ---
**Author:** ![ThoML](https://avatars.discourse-cdn.com/v4/letter/t/d78d45/32.png) [@ThoML](https://rubytalk.org/u/ThoML)\ **Post date:** [29 February 2008 04:44 UTC](https://rubytalk.org/t/proc-new-and-return/44832/10 "2008-02-29T04:44:56Z")
> it was new news to meet the semantics of `proc' differed from Proc.new > so radically! Well, that was my point and what my example was supposed to demonstrate: in ruby18, proc is a synonym for lambda but in ruby19 it's an alias for Proc.new. [http://eigenclass.org/hiki/Changes+in+Ruby+1.9#l47](http://eigenclass.org/hiki/Changes+in+Ruby+1.9#l47) Regards, Thomas.