Rails - Nov 2006 - Can someone please explain this line of code?

>From Agile Rails Development:
current_item = @items.find {|item| item.product == product}

it''s at the start of the "add_product" method in the model
"cart"


--~--~---------~--~----~------------~-------~--~----~
 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?hl=en
-~----------~----~----~----~------~----~------~--~---

On Nov 29, 2006, at 8:25 PM, Brandon wrote:
> current_item = @items.find {|item| item.product == product}
>
> it''s at the start of the "add_product" method in the
model "cart"

It finds an entry in the @items list whose product attribute equals  
the parameter product. If none exists, it sets current_item to nil.


Dave

--~--~---------~--~----~------------~-------~--~----~
 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?hl=en
-~----------~----~----~----~------~----~------~--~---

Dave Thomas wrote:
> On Nov 29, 2006, at 8:25 PM, Brandon wrote:
> 
>> current_item = @items.find {|item| item.product == product}
>>
>> it''s at the start of the "add_product" method in the
model "cart"
> 
> 
> It finds an entry in the @items list whose product attribute equals
> the parameter product. If none exists, it sets current_item to nil.
> 
> 
> Dave
Do I detect that Dave has some free time now that the book has gone to 
the publisher?  Wait, I think I hear Rails 2.0 calling....

-- 
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?hl=en
-~----------~----~----~----~------~----~------~--~---

Thank you!

The book rocks by the way!


--~--~---------~--~----~------------~-------~--~----~
 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?hl=en
-~----------~----~----~----~------~----~------~--~---

On Nov 29, 2006, at 9:05 PM, Bill wrote:
> Do I detect that Dave has some free time now that the book has gone to
> the publisher?  Wait, I think I hear Rails 2.0 calling....

Get thee behind me, Satan...

--~--~---------~--~----~------------~-------~--~----~
 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?hl=en
-~----------~----~----~----~------~----~------~--~---

Brandon Wright wrote:
>>From Agile Rails Development:
> 
> current_item = @items.find {|item| item.product == product}
> 
> it''s at the start of the "add_product" method in the
model "cart"
I suppose it takes a pair of brass ones to reply to this right after 
somebody who claims to be Dave Thomas, but I think I can add to his 
answer.  It is a bit ironic that Dave answered this, since Brandon''s 
lack of understanding is almost certainly due to not having read Dave''s
book on Ruby.

Brandon, you should do yourself a favor and read Dave''s
"PickAxe" book
called Programming Ruby.  It will make learning Rails much easier.

Meanwhile, to get you through this one, let me just add that this 
probably looks "wierd" to you because you are not familiar yet with a 
common Ruby thing called an "iterator".  It is basically a method 
(function) that makes it ridiculously easy to step through all of the 
items in a list (or in this case a table of a database), and do 
something with each item.  It''s sort of a for loop without all the 
extraneous nonsense.  The object knows how to iterate over it''s items, 
all you have to supply is the little block of code that says what to do 
with each one.

So here, the iterator "find" (which "items" inherits from
the
ActiveRecord class that all Rails models belong to) feeds all of the 
"items" in the database to the block of code in the braces one at a
time
and lets that block compare the product attribute of the item to the 
"product" parameter that was passed in.  The block just looks for an 
item where the product field equals the one we are looking for.  The 
block of code returns true or false for each "iteration", and when it 
returns true, the "find" method says "oh, that''s the one
you were
looking for, and returns it.  If it doesn''t ever see a "true"
from the
block, and it runs out of items to iterate over, it gives up and returns 
nil.

The unusual looking |item| construct at the beginning of the code block 
is just how Ruby allows the programmer to say "for each one of the 
things you''re about to pass me, I''m going to call them
''item'' in this
code block".  The code block could just as easily been {|Dave| 
Dave.product == product} and it would work the same way.  Using "item"
just makes more sense.

How''d I do Dave?

jp


-- 
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?hl=en
-~----------~----~----~----~------~----~------~--~---

Hi --

On Thu, 30 Nov 2006, Jeff Pritchard wrote:
> The unusual looking |item| construct at the beginning of the code block
> is just how Ruby allows the programmer to say "for each one of the
> things you''re about to pass me, I''m going to call them
''item'' in this
> code block".
It also has implications if you already have a variable called item --
namely, it will assign to *that* variable.  (In Ruby 1.8 and earlier,
that is.)  That can be advantageous (which is why I''m sad that
it''s
disappearing), but also means one has to be careful in choosing a
variable name since it could have an effect outside the block.
> The code block could just as easily been {|Dave|
> Dave.product == product} and it would work the same way.  Using
"item"
> just makes more sense.
You wouldn''t want to use a constant there, though.  It will run, but
you''ll get warnings.
> How''d I do Dave?
Whoops, I''m the wrong Dav(e|id).  I''m just pinch-hitting :-)


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?hl=en
-~----------~----~----~----~------~----~------~--~---

Thanks for taking the time to write that reply - Unfortunately I can''t
read that many books all at once, although I''d point out that Dave
Thomas is co-author (with DHH) of the book I am going through (Agile
Web Development with Rails 2nd Ed.). I''ll get to "Programming
Ruby"
soon enough, I''m pretty much addicted to how cool this framework is.

I think it''s great that everyone is so involved in the community that a
newbie like me posts a rather basic question, and gets replys from two
very notable Dave''s (Thomas and Black) and a very well thought out
response from you.

Thanks everyone!!


--~--~---------~--~----~------------~-------~--~----~
 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?hl=en
-~----------~----~----~----~------~----~------~--~---

Thanks for taking the time to write that reply - Unfortunately I can''t
read that many books all at once, although I''d point out that Dave
Thomas is co-author (with DHH) of the book I am going through (Agile
Web Development with Rails 2nd Ed.). I''ll get to "Programming
Ruby"
soon enough, I''m pretty much addicted to how cool this framework is.

I think it''s great that everyone is so involved in the community that a
newbie like me posts a rather basic question, and gets replys from two
very notable Dave''s (Thomas and Black) and a very well thought out
response from you.

Thanks everyone!!


--~--~---------~--~----~------------~-------~--~----~
 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?hl=en
-~----------~----~----~----~------~----~------~--~---