# Block\_given? problem **URL:** \ **Category:** ruby-talk\ **Created:** [20 July 2007 11:19 UTC](https://rubytalk.org/t/block-given-problem/39267 "2007-07-20T11:19:58Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Westlin9](https://avatars.discourse-cdn.com/v4/letter/w/ac91a4/32.png) [@Westlin9](https://rubytalk.org/u/Westlin9)\ **Post date:** [20 July 2007 11:19 UTC](https://rubytalk.org/t/block-given-problem/39267/1 "2007-07-20T11:19:58Z")
I can't figure out why the do...end block isn't detected by the "block\_given?" function. The problem occurs when a method call with a block is used in a puts statement. See the code example below. Can some one explain this to me please? Is this a bug? class TheClass   def self.TheMethod()     if block\_given?       puts "yes, block given"     else       puts "no block is given"     end     'return val'   end end # ok puts TheClass.TheMethod {|param| 123} # block not detected puts TheClass.TheMethod do |param|   123 end # ok a = TheClass.TheMethod {|param| 123} puts a # ok a = TheClass.TheMethod do |param|   123 end puts a ---
**Author:** ![Forum](https://avatars.discourse-cdn.com/v4/letter/f/43a26b/32.png) [@Forum](https://rubytalk.org/u/Forum)\ **Post date:** [20 July 2007 12:04 UTC](https://rubytalk.org/t/block-given-problem/39267/2 "2007-07-20T12:04:00Z")
puts( TheClass.TheMethod do nil end ) do...end and {} do not have the same precedence, thus, without the () you are doing this puts( TheClass.TheMethod ) do nil end HTH Robert > **···** > > On 7/20/07, westlin9@gmail.com \ wrote: > > > I can't figure out why the do...end block isn't detected by the > > "block\_given?" function. The problem occurs when a method call with a > > block is used in a puts statement. See the code example below. > > Can some one explain this to me please? Is this a bug? > > > > class TheClass > >   def self.TheMethod() > >     if block\_given? > >       puts "yes, block given" > >     else > >       puts "no block is given" > >     end > >     'return val' > >   end > > end > > > > # ok > > puts TheClass.TheMethod {|param| 123} > > > > # block not detected > > puts TheClass.TheMethod do |param| > >   123 > > end > > > > # ok > > a = TheClass.TheMethod {|param| 123} > > puts a > > > > # ok > > a = TheClass.TheMethod do |param| > >   123 > > end > > puts a > > -- > I always knew that one day Smalltalk would replace Java. > I just didn't know it would be called Ruby > -- Kent Beck ---
**Author:** ![Mariusz\_Pekala](https://avatars.discourse-cdn.com/v4/letter/m/7ba0ec/32.png) [@Mariusz\_Pekala](https://rubytalk.org/u/Mariusz_Pekala)\ **Post date:** [20 July 2007 12:46 UTC](https://rubytalk.org/t/block-given-problem/39267/3 "2007-07-20T12:46:24Z")
> I can't figure out why the do...end block isn't detected by the > "block\_given?" function. The problem occurs when a method call with a > block is used in a puts statement. See the code example below. > Can some one explain this to me please? Is this a bug? > > class TheClass >   def self.TheMethod() >     if block\_given? >       puts "yes, block given" >     else >       puts "no block is given" >     end >     'return val' >   end > end > > # ok > puts TheClass.TheMethod {|param| 123} > > # block not detected > puts TheClass.TheMethod do |param| >   123 > end This is because do..end block gets attached to the 'puts' instead of TheMethod. do..end and {||..} differ in precedence. {||..} binds to the rightmost method, while do..end to the leftmost one. > # ok > a = TheClass.TheMethod {|param| 123} > puts a > > # ok > a = TheClass.TheMethod do |param| >   123 > end > puts a There you have no ambiguity as there is only one method call. > **···** > > On 2007-07-20 20:19:58 +0900 (Fri, Jul), westlin9@gmail.com wrote: > > -- > No virus found in this outgoing message. > Checked by 'grep -i virus $MESSAGE' > Trust me. ---
**Author:** ![Westlin9](https://avatars.discourse-cdn.com/v4/letter/w/ac91a4/32.png) [@Westlin9](https://rubytalk.org/u/Westlin9)\ **Post date:** [20 July 2007 12:20 UTC](https://rubytalk.org/t/block-given-problem/39267/4 "2007-07-20T12:20:01Z")
Thanks > **···** > > On 20 Juli, 14:04, "Robert Dober" \ wrote: > > > On 7/20/07, westl...@gmail.com \ wrote: > > > > \> I can't figure out why the do...end block isn't detected by the > > \> "block\_given?" function. The problem occurs when a method call with a > > \> block is used in a puts statement. See the code example below. > > \> Can some one explain this to me please? Is this a bug? > > > > \> class TheClass > > \> def self.TheMethod() > > \> if block\_given? > > \> puts "yes, block given" > > \> else > > \> puts "no block is given" > > \> end > > \> 'return val' > > \> end > > \> end > > > > \> # ok > > \> puts TheClass.TheMethod {|param| 123} > > > > \> # block not detected > > \> puts TheClass.TheMethod do |param| > > \> 123 > > \> end > > > > \> # ok > > \> a = TheClass.TheMethod {|param| 123} > > \> puts a > > > > \> # ok > > \> a = TheClass.TheMethod do |param| > > \> 123 > > \> end > > \> puts a > > > > puts( TheClass.TheMethod do nil end ) > > > > do...end and {} do not have the same precedence, thus, without the () > > you are doing this > > puts( TheClass.TheMethod ) do nil end > > > > HTH > > Robert > > > > -- > > I always knew that one day Smalltalk would replace Java. > > I just didn't know it would be called Ruby > > -- Kent Beck- Dölj citerad text - > > > > - Visa citerad text - ---
**Author:** ![Rick\_DeNatale1](https://avatars.discourse-cdn.com/v4/letter/r/bbce88/32.png) [@Rick\_DeNatale1](https://rubytalk.org/u/Rick_DeNatale1)\ **Post date:** [20 July 2007 18:13 UTC](https://rubytalk.org/t/block-given-problem/39267/5 "2007-07-20T18:13:37Z")
do..end vs {} and vs. && or vs. || not vs ! I think that it can be said that generally in ruby "symbols bind tighter than words" > **···** > > On 7/20/07, Robert Dober \ wrote: > > > do...end and {} do not have the same precedence, thus, without the () > > you are doing this > > puts( TheClass.TheMethod ) do nil end > > -- > Rick DeNatale > > My blog on Ruby > [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)