Rails - Dec 2006 - Simple syntax question

In:

=== code start ===a=10, b=20
c=100, d=2200
#x=>1000, y=>2000 # MultipleExpressionsPerLine.rb:3:

p a, b
p c, d
=== code end ==
Ruby puts out four lines (under SciTE):

[10, 20]
20
[100, 2200]
2200

Q1: Why does Ruby somehow create an array for lines 1 & 2?
Q2: Why does Ruby assign this array to a, but the scalar (20) to b?
Q3: If Ruby''s willing to build arrays for lines 1 & 2, why
won''t it
build a hash for line 3?

I''m running WinXP-Pro/SP2, Ruby 1.8.2-15, Rails  1.1.6.


--~--~---------~--~----~------------~-------~--~----~
 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 Fri, 15 Dec 2006, Richard wrote:
>
> In:
>
> === code start ===> a=10, b=20
> c=100, d=2200
> #x=>1000, y=>2000 # MultipleExpressionsPerLine.rb:3:
>
> p a, b
> p c, d
> === code end ==>
> Ruby puts out four lines (under SciTE):
>
> [10, 20]
> 20
> [100, 2200]
> 2200
>
> Q1: Why does Ruby somehow create an array for lines 1 & 2?
> Q2: Why does Ruby assign this array to a, but the scalar (20) to b?
> Q3: If Ruby''s willing to build arrays for lines 1 & 2, why
won''t it
> build a hash for line 3?
>
> I''m running WinXP-Pro/SP2, Ruby 1.8.2-15, Rails  1.1.6.
When you do this:

   a=10, b=20

the way it''s parsed is:

   a = 10, (b=20)

The assignment of 20 to b happens first, and then the whole rhs is
assigned to a.  From a''s point of view, this is the same as:

   a = 10,20

and assigning a literal list like that works like assigning an array.

As for the third line: x => 1000 isn''t a legal expression on its
own.
=> is not an assignment operator; it''s just a hash key/value
separator.


David

-- 
Q. What''s a good holiday present for the serious Rails developer?
A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black)
    aka The Ruby book for Rails developers!
Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
A. Ruby Power and Light, LLC (http://www.rubypal.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 David,

Thanks for your clarification.  Now that you explain (a=10, b=20),  my
brain said: You read that before, Dummy ... why do you always forget
things?

I had just found a nice tutorial on sorting tables by clicking on
column headings.  It included a long line of comma-separated
assignments and I couldn''t make sense of it.  Now I''m grounded
again!

Again, thanks.

Best wishes,
Richard

dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org wrote:
> Hi --
>
> On Fri, 15 Dec 2006, Richard wrote:
>
> >
> > In:
> >
> > === code start ===> > a=10, b=20
> > c=100, d=2200
> > #x=>1000, y=>2000 # MultipleExpressionsPerLine.rb:3:
> >
> > p a, b
> > p c, d
> > === code end ==> >
> > Ruby puts out four lines (under SciTE):
> >
> > [10, 20]
> > 20
> > [100, 2200]
> > 2200
> >
> > Q1: Why does Ruby somehow create an array for lines 1 & 2?
> > Q2: Why does Ruby assign this array to a, but the scalar (20) to b?
> > Q3: If Ruby''s willing to build arrays for lines 1 & 2,
why won''t it
> > build a hash for line 3?
> >
> > I''m running WinXP-Pro/SP2, Ruby 1.8.2-15, Rails  1.1.6.
>
> When you do this:
>
>    a=10, b=20
>
> the way it''s parsed is:
>
>    a = 10, (b=20)
>
> The assignment of 20 to b happens first, and then the whole rhs is
> assigned to a.  From a''s point of view, this is the same as:
>
>    a = 10,20
>
> and assigning a literal list like that works like assigning an array.
>
> As for the third line: x => 1000 isn''t a legal expression on
its own.
> => is not an assignment operator; it''s just a hash key/value
> separator.
>
>
> David
>
> --
> Q. What''s a good holiday present for the serious Rails developer?
> A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black)
>     aka The Ruby book for Rails developers!
> Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
> A. Ruby Power and Light, LLC (http://www.rubypal.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
-~----------~----~----~----~------~----~------~--~---