thr3ads.net - Rails - Yield Example in Ruby For Rails book [Oct 2006]

If this information is useful, please help other people find it:
Share via:

Bala Paranj

2006-Oct-07 01:15 UTC

Yield Example in Ruby For Rails book

I am going through the Ruby for Rails book. How do I run the following code:

class C 
 
  def temp_chart(temps) 
    for temp in temps
      converted = yield(temp)
      puts "#{temp}\t#{converted}"
    end
  end
  
  celsiuses = [0,10,20,40]
  temp_chart(celsiuses) {|cel| cel * 9 / 5 + 32} 
  
end

c = C.new
c.temp_chart(celsiuses)

  
I am getting error message: 

NoMethodError: undefined method temp_chart for C:Class

at top level	in c.rb at line 11

TIA

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

Daniel Higginbotham

2006-Oct-07 01:44 UTC

head link

Re: Yield Example in Ruby For Rails book

You probably want

class C
  def temp_chart(temps)
    for temp in temps
      converted = yield(temp)
      puts "#{temp}\t#{converted}"
    end
  end
end

celsiuses = [0,10,20,40]

c = C.new
c.temp_chart(celsiuses)


I probably can''t explain _why_ very well, but eventually Ruby for Rails
will.

Good luck!

On Friday 06 October 2006 3:15 pm, Bala Paranj wrote:> I am going through the Ruby for Rails book. How do I run the following
> code:
>
> class C
>
>   def temp_chart(temps)
>     for temp in temps
>       converted = yield(temp)
>       puts "#{temp}\t#{converted}"
>     end
>   end
>
>   celsiuses = [0,10,20,40]
>   temp_chart(celsiuses) {|cel| cel * 9 / 5 + 32}
>
> end
>
> c = C.new
> c.temp_chart(celsiuses)
>
>
> I am getting error message:
>
> NoMethodError: undefined method temp_chart for C:Class
>
> at top level	in c.rb at line 11
>
> TIA
>
> 
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org

2006-Oct-07 01:51 UTC

head link

Re: Yield Example in Ruby For Rails book

Hi --

On Fri, 6 Oct 2006, Bala Paranj wrote:
>
> I am going through the Ruby for Rails book. How do I run the following
code:
>
> class C
>
>  def temp_chart(temps)
>    for temp in temps
>      converted = yield(temp)
>      puts "#{temp}\t#{converted}"
>    end
>  end
>
>  celsiuses = [0,10,20,40]
>  temp_chart(celsiuses) {|cel| cel * 9 / 5 + 32}
>
> end
>
> c = C.new
> c.temp_chart(celsiuses)
>
>
> I am getting error message:
>
> NoMethodError: undefined method temp_chart for C:Class
>
> at top level	in c.rb at line 11
Your combining two ways of doing it that don''t mix; you want either
this:

   class C
     def something
     end
   end

   c = C.new
   c.something

or this:

   def something
   end

   something

What you''re trying to do is like this:

   class C
     def something
     end

     something    # won''t run in this context; it needs an
                  # instance of C
   end

Also, note that celsiuses is a local variable, so the celsiuses inside
the class definition block won''t be the same as the celsiuses outside
it.


David

-- 
                   David A. Black |
dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org
Author of "Ruby for Rails"   [1] | Ruby/Rails training &
consultancy [3]
DABlog (DAB''s Weblog)        [2] | Co-director, Ruby Central, Inc.  
[4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

Bala Paranj

2006-Oct-07 07:32 UTC

head link

Re: Yield Example in Ruby For Rails book

I ran the code as given in the book:

def temp_chart(temps) 
  for temp in temps 
    converted = yield(temp) 
    puts "#{temp}\t#{converted}" 
  end 
end 
celsiuses = [0,10,20,30,40,50,60,70,80,90,100] 
temp_chart(celsiuses) {|cel| cel * 9 / 5 + 32 } 

This runs fine. I was under the impression it must be part of a class. I am
still confused how I
could use yield from within a class. Where should the yield block be defined?



--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

Bala Paranj

2006-Oct-07 07:39 UTC

head link

Re: Yield Example in Ruby For Rails book

When I run that code I get:

LocalJumpError: no block given

method temp_chart	in c.rb at line 5
method temp_chart	in c.rb at line 4
at top level	in c.rb at line 13


--- Daniel Higginbotham
<daniel-4cOk6EWy6wjNj93mkU9IYrqjc7CnNF17@public.gmane.org> wrote:
> You probably want
> 
> class C
>   def temp_chart(temps)
>     for temp in temps
>       converted = yield(temp)
>       puts "#{temp}\t#{converted}"
>     end
>   end
> end
> 
> celsiuses = [0,10,20,40]
> 
> c = C.new
> c.temp_chart(celsiuses)
> 
> 
> I probably can''t explain _why_ very well, but eventually Ruby for
Rails will.
> 
> Good luck!
> 
> On Friday 06 October 2006 3:15 pm, Bala Paranj wrote:
> > I am going through the Ruby for Rails book. How do I run the following
> > code:
> >
> > class C
> >
> >   def temp_chart(temps)
> >     for temp in temps
> >       converted = yield(temp)
> >       puts "#{temp}\t#{converted}"
> >     end
> >   end
> >
> >   celsiuses = [0,10,20,40]
> >   temp_chart(celsiuses) {|cel| cel * 9 / 5 + 32}
> >
> > end
> >
> > c = C.new
> > c.temp_chart(celsiuses)
> >
> >
> > I am getting error message:
> >
> > NoMethodError: undefined method temp_chart for C:Class
> >
> > at top level	in c.rb at line 11
> >
> > TIA
> >
> > 
> 
> > 

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

Florian Aßmann

2006-Oct-07 09:01 UTC

head link

Re: Yield Example in Ruby For Rails book

That gave me an idea, ha, this looks like some kind_of? class  
initialization... :D

class X
     def self.ordinary_class_method_is_to(&block)
         block.call
     end
     def ordinary_instance_method_is_to(&block)
         block.call
     end

     ordinary_class_method_is_to do
         puts ''Buy bags...''
     end
end

x = X.new
x.ordinary_instance_method_is_to do
     puts ''Give away...''
end


Am 07.10.2006 um 09:39 schrieb Bala Paranj:
>
> When I run that code I get:
>
> LocalJumpError: no block given
>
> method temp_chart	in c.rb at line 5
> method temp_chart	in c.rb at line 4
> at top level	in c.rb at line 13
>
>
> --- Daniel Higginbotham
<daniel-4cOk6EWy6wjNj93mkU9IYrqjc7CnNF17@public.gmane.org> wrote:
>
>> You probably want
>>
>> class C
>>   def temp_chart(temps)
>>     for temp in temps
>>       converted = yield(temp)
>>       puts "#{temp}\t#{converted}"
>>     end
>>   end
>> end
>>
>> celsiuses = [0,10,20,40]
>>
>> c = C.new
>> c.temp_chart(celsiuses)
>>
>>
>> I probably can''t explain _why_ very well, but eventually Ruby
for
>> Rails will.
>>
>> Good luck!
>>
>> On Friday 06 October 2006 3:15 pm, Bala Paranj wrote:
>>> I am going through the Ruby for Rails book. How do I run the  
>>> following
>>> code:
>>>
>>> class C
>>>
>>>   def temp_chart(temps)
>>>     for temp in temps
>>>       converted = yield(temp)
>>>       puts "#{temp}\t#{converted}"
>>>     end
>>>   end
>>>
>>>   celsiuses = [0,10,20,40]
>>>   temp_chart(celsiuses) {|cel| cel * 9 / 5 + 32}
>>>
>>> end
>>>
>>> c = C.new
>>> c.temp_chart(celsiuses)
>>>
>>>
>>> I am getting error message:
>>>
>>> NoMethodError: undefined method ‘temp_chart’ for C:Class
>>>
>>> at top level	in c.rb at line 11
>>>
>>> TIA
>>>
>>>
>>
>>>
>
>
> >

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

Huw Collingbourne

2006-Oct-07 10:44 UTC

head link

Re: Yield Example in Ruby For Rails book

Hello, try this:

class C

  def temp_chart(temps)
    for temp in temps
      converted = yield(temp)
      puts "#{temp}\t#{converted}"
    end
  end
end

celsiuses = [0,10,20,40]

c = C.new
c.temp_chart(celsiuses) {|cel| cel * 9 / 5 + 32}



Explanation:
temps is an array argument (supplied here by celsiuses)

the method temp_chart also takes a block of executable code. That is 
this:
   {|cel| cel * 9 / 5 + 32}
It is this block of code which is executed when yield is used here:
   yield(temp)
The block conatains a variable, cel, to which the elements of the 
celsiuses array (from the array argument named temps) will be passed, 
just like calling a named method with an array argument.

Blocks can be tricky to understand. Just remember that they work a bit 
like unnamed functions that can be passed to methods. When the method 
receives the block it can call the block using yield. The block 
arguments (here cel) are like the formal arguments to a named method. 
When yield specifies an argument (here temp) it has the effect of 
calling the block and passing to it the named argument.

best wishes
Huw

Ruby In Steel
Ruby Programming With Visual Studio
http://www.sapphiresteel.com

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

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org

2006-Oct-07 11:43 UTC

head link

Re: Yield Example in Ruby For Rails book

Hi --

On Fri, 6 Oct 2006, Daniel Higginbotham wrote:
>
> On Friday 06 October 2006 3:15 pm, Bala Paranj wrote:
>> I am going through the Ruby for Rails book. How do I run the following
>> code:
>>
>> class C
>>
>>   def temp_chart(temps)
>>     for temp in temps
>>       converted = yield(temp)
>>       puts "#{temp}\t#{converted}"
>>     end
>>   end
>>
>>   celsiuses = [0,10,20,40]
>>   temp_chart(celsiuses) {|cel| cel * 9 / 5 + 32}
>>
>> end
>>
>> c = C.new
>> c.temp_chart(celsiuses)
>>
>>
>> I am getting error message:
>>
>> NoMethodError: undefined method temp_chart for C:Class
>>
>> at top level	in c.rb at line 11
>>
> You probably want
>
> class C
>  def temp_chart(temps)
>    for temp in temps
>      converted = yield(temp)
>      puts "#{temp}\t#{converted}"
>    end
>  end
> end
>
> celsiuses = [0,10,20,40]
>
> c = C.new
> c.temp_chart(celsiuses)
>
>
> I probably can''t explain _why_ very well, but eventually Ruby for
Rails will.
You need a block, though :-)


David

-- 
                   David A. Black |
dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org
Author of "Ruby for Rails"   [1] | Ruby/Rails training &
consultancy [3]
DABlog (DAB''s Weblog)        [2] | Co-director, Ruby Central, Inc.  
[4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

Bala Paranj

2006-Oct-07 13:27 UTC

head link

Re: Yield Example in Ruby For Rails book

Thank you for your explanation. It works!!! I don''t know why any of the
authors who write Ruby
books use Java and the known concepts to learn this new language. It is much
easier to learn that
way. 

So this block thingy is kinda like anonymous classes?

Rails for Java developers is in beta, who is writing Ruby for Java Developers? 

--- Huw Collingbourne
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:
> 
> Hello, try this:
> 
> class C
> 
>   def temp_chart(temps)
>     for temp in temps
>       converted = yield(temp)
>       puts "#{temp}\t#{converted}"
>     end
>   end
> end
> 
> celsiuses = [0,10,20,40]
> 
> c = C.new
> c.temp_chart(celsiuses) {|cel| cel * 9 / 5 + 32}

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org

2006-Oct-07 13:31 UTC

head link

Re: Yield Example in Ruby For Rails book

Hi --

On Sat, 7 Oct 2006, Bala Paranj wrote:
>
> Thank you for your explanation. It works!!! I don''t know why any
of
> the authors who write Ruby books use Java and the known concepts to
> learn this new language. It is much easier to learn that
> way.
Do you mean why they *don''t* use Java?  In my case it''s
because I
don''t know Java, and also I really want to write about Ruby.  Maybe
I''ll change my mind when someone writes Java for Ruby Developers :-)


David

-- 
                   David A. Black |
dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org
Author of "Ruby for Rails"   [1] | Ruby/Rails training &
consultancy [3]
DABlog (DAB''s Weblog)        [2] | Co-director, Ruby Central, Inc.  
[4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

Bala Paranj

2006-Oct-07 13:51 UTC

head link

Re: Yield Example in Ruby For Rails book

> I''ll change my mind when someone writes Java for Ruby Developers
:-)
> 
David your book is kinda like a good wine. It is getting better as it ages on my
Mac. I am reading
it the second time slowly and also running the examples. I understood your
explanation about
blocks, scopes etc. But only when I run the examples my brain is able to fully
absorb the material
in the book.

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org

2006-Oct-07 13:54 UTC

head link

Re: Yield Example in Ruby For Rails book

Hi --

On Sat, 7 Oct 2006, Bala Paranj wrote:
>
>
>> I''ll change my mind when someone writes Java for Ruby
Developers :-)
>>
>
> David your book is kinda like a good wine. It is getting better as
> it ages on my Mac. I am reading it the second time slowly and also
> running the examples. I understood your explanation about
> blocks, scopes etc. But only when I run the examples my brain is
> able to fully absorb the material in the book.
That''s fine -- it''s all part of it.  Running the examples
isn''t
"cheating" :-)

I''m glad you''re liking it.


David
> >
-- 
                   David A. Black |
dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org
Author of "Ruby for Rails"   [1] | Ruby/Rails training &
consultancy [3]
DABlog (DAB''s Weblog)        [2] | Co-director, Ruby Central, Inc.  
[4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

Huw Collingbourne

2006-Oct-07 14:10 UTC

head link

Re: Yield Example in Ruby For Rails book

Bala Paranj wrote:> So this block thingy is kinda like anonymous classes?
In principle they are anonymous *methods* rather than *classes*. If you 
think of them like that it should be easier to understand what''s going 
on when you pass arguments into them and these arguments initialize the 
block variables between the upright bars (like |cel| in the example 
above).

Blocks are kind of oddities (in my view!) in Ruby, however, as they 
aren''t objects. True, they can be wrapped up inside objects (Procs) but
that doesn''t alter the fact that a block itself has no independent 
existence. This contrasts with some other object oriented languages - 
notably Smalltalk - in which a block is an object with its own methods. 
Ask a standalone Smalltalk block to tell you its class and it will reply 
that it is an instance of Block (or BlockClosure). Ask a standalone Ruby 
block to tell you its class - e.g.

puts( {|cel| cel * 9 / 5 + 32}.class )

...and Ruby replies:

parse error, unexpected ''|'', expecting ''}''
puts( {|cel| cel * 9 / 5 + 32}.class )

However, I may be straying into arcane areas here ;-)

Keep things simple: think of blocks as anonymous methods that can be 
''called'' using ''yield'' and you
won''t go too far wrong.

best wishes
Huw

Ruby In Steel
Ruby Programming With Visual Studio
http://www.sapphiresteel.com

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

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

Bala Paranj

2006-Oct-07 14:32 UTC

head link

Re: Yield Example in Ruby For Rails book

I found the fix, the problem is that it was expecting the block: {|cel| cel * 9
/ 5 + 32}
after the name. Now it runs fine.

> > When I run that code I get:
> >
> > LocalJumpError: no block given
> >
> > method temp_chart	in c.rb at line 5
> > method temp_chart	in c.rb at line 4
> > at top level	in c.rb at line 13
> >
> >
> > --- Daniel Higginbotham
<daniel-4cOk6EWy6wjNj93mkU9IYrqjc7CnNF17@public.gmane.org> wrote:
> >
> >> You probably want
> >>
> >> class C
> >>   def temp_chart(temps)
> >>     for temp in temps
> >>       converted = yield(temp)
> >>       puts "#{temp}\t#{converted}"
> >>     end
> >>   end
> >> end
> >>
> >> celsiuses = [0,10,20,40]
> >>
> >> c = C.new
> >> c.temp_chart(celsiuses)

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org

2006-Oct-07 15:01 UTC

head link

Re: Yield Example in Ruby For Rails book

Hi --

On Sat, 7 Oct 2006, Huw Collingbourne wrote:
>
> Bala Paranj wrote:
>> So this block thingy is kinda like anonymous classes?
>
> In principle they are anonymous *methods* rather than *classes*. If you
> think of them like that it should be easier to understand what''s
going
> on when you pass arguments into them and these arguments initialize the
> block variables between the upright bars (like |cel| in the example
> above).
Thinking of them as methods has some pitfalls, though, since methods
always live in modules or classes and blocks don''t.
> Blocks are kind of oddities (in my view!) in Ruby, however, as they
> aren''t objects. True, they can be wrapped up inside objects
(Procs) but
> that doesn''t alter the fact that a block itself has no independent
> existence. This contrasts with some other object oriented languages -
> notably Smalltalk - in which a block is an object with its own methods.
> Ask a standalone Smalltalk block to tell you its class and it will reply
> that it is an instance of Block (or BlockClosure). Ask a standalone Ruby
> block to tell you its class - e.g.
>
> puts( {|cel| cel * 9 / 5 + 32}.class )
>
> ...and Ruby replies:
>
> parse error, unexpected ''|'', expecting
''}''
> puts( {|cel| cel * 9 / 5 + 32}.class )
>
> However, I may be straying into arcane areas here ;-)
I think the best way to look at blocks is as a part of the syntax of
the Ruby method call:

   [receiver  dot]  method_name  [arg_list]  [block]

Informally one does speak of blocks as anonymous functions, rather
than saying "a syntactic construct that gets wrapped in a Proc" (or
whatever).  But it''s useful to keep the distinction in view that they
start life as syntax.

On that construction, a block is a kind of sibling to the argument
list -- and, in both cases, they''re pure syntax: there''s no
Block
class and no ArgumentList class.  Also in both cases, the method can
grab what''s there and stash it in a variable:

      m(a,b,c) { puts "hi" }
        | | |  |
  def m(x,y,z,&block)

In a sense, the &block thing is really a completely separate
transaction from the x,y,z part; it might almost be represented as:

   def m(x,y,z) {&block}

or something.  (I''m not advocating that, just making the point that
the block and &block are going on in parallel to, rather than as part
of, the passing of arguments.)


David

-- 
                   David A. Black |
dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org
Author of "Ruby for Rails"   [1] | Ruby/Rails training &
consultancy [3]
DABlog (DAB''s Weblog)        [2] | Co-director, Ruby Central, Inc.  
[4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

Huw Collingbourne

2006-Oct-07 15:27 UTC

head link

Re: Yield Example in Ruby For Rails book

unknown wrote:> Thinking of them as methods has some pitfalls, though, since methods
> always live in modules or classes and blocks don''t.
> 
That''s true. In that case, thinking of them as anonymous *functions* 
might be a better model. Then again, thinking of
''free-floating''
functions in a rigorously OOP language raises its own problems ;-)
> On that construction, a block is a kind of sibling to the argument
> list -- and, in both cases, they''re pure syntax:
I must say that I have problems with making Ruby''s blocks fit 
comfortably into the Ruby universe. The arguments in an argument list 
act as the receivers of the arguments passed in the ''message''
sent to
that method. These formal arguments are therefore, as you say, ''pure 
syntax''. However, the objects to which the arguments are instantiated 
are *not* mere syntax. They have a ''real'' self-contained
existence as
instances of Ruby classes. Blocks, on the other hand, do not have such 
an existence.

I must say that I am very much prejudiced in favour of the Smalltalk 
version of blocks (instances of a Block or Closure class) as that simply 
seems to me to be consistent with the pure OOP paradigm.

That said, Ruby is by no means as strictly object oriented as Smalltalk 
(compare its fairly permissive approach to encapsulation, for example), 
which possibly explains why blocks are treated in this way.

best wishes
Huw

Ruby In Steel
Ruby Programming With Visual Studio
http://www.sapphiresteel.com

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

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org

2006-Oct-07 15:35 UTC

head link

Re: Yield Example in Ruby For Rails book

Hi --

On Sat, 7 Oct 2006, Huw Collingbourne wrote:
> I must say that I have problems with making Ruby''s blocks fit
> comfortably into the Ruby universe. The arguments in an argument list
> act as the receivers of the arguments passed in the
''message'' sent to
> that method. These formal arguments are therefore, as you say,
''pure
> syntax''.
I meant the argument list that''s part of the method call (rather than
the method).  I should probably be saying parameter instead of
argument or something... but basically the (a,b,c) in meth(a,b,c).
> However, the objects to which the arguments are instantiated
> are *not* mere syntax. They have a ''real'' self-contained
existence as
> instances of Ruby classes. Blocks, on the other hand, do not have such
> an existence.
>
> I must say that I am very much prejudiced in favour of the Smalltalk
> version of blocks (instances of a Block or Closure class) as that simply
> seems to me to be consistent with the pure OOP paradigm.
I believe that there was a Block class in CVS head two or three years
ago, for about a week :-)  I further remember that its existence had
something to do with my having lobbied for it, though I can''t remember
the sequence in detail.  It was a period when there was a lot of
discussion of the weirdnesses of Proc/proc/lambda/block/method.  The
discussion doesn''t seem to be as lively any more, though at least some
of the weirdness is still there :-)


David

-- 
                   David A. Black |
dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org
Author of "Ruby for Rails"   [1] | Ruby/Rails training &
consultancy [3]
DABlog (DAB''s Weblog)        [2] | Co-director, Ruby Central, Inc.  
[4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

Bala Paranj

2006-Oct-07 22:50 UTC

head link

Re: Yield Example in Ruby For Rails book

--- dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org
wrote:> > In principle they are anonymous *methods* rather than *classes*. If
you
> > think of them like that it should be easier to understand
what''s going
> > on when you pass arguments into them and these arguments initialize
the
> > block variables between the upright bars (like |cel| in the example
> > above).
> 
> Thinking of them as methods has some pitfalls, though, since methods
> always live in modules or classes and blocks don''t.
>   This is a very good observation. You said in the book that one of the
advantages of the blocks
is that they can be combined in many ways. I did not find any example of how you
would combine it.

I am not clear on how you would combine it since it is not part of a class or
module.

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

Rails - Oct 2006 - Yield Example in Ruby For Rails book

Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book

Re: Yield Example in Ruby For Rails book