Ruby Forum Ruby > Problem with case statements

I have an innocent looking code:

54:    def find(*args)
55:      options = args.extract_options!
56:      validate_find_options(options)
57:      case args.first
58:      when :first: find_first(options)
59:      when :all: find_all(options)
60:      else raise "Invalid find"
61:      end
62:    end


Now, above case statement totally blows up with Ruby 1.9:

/home/hemant/push_server/lib/db_connection.rb:61: warning: else without
rescue is useless
/home/hemant/push_server/bin/boot.rb:34:in
`require': /home/hemant/push_server/lib/db_connection.rb:58: syntax
error, unexpected ':', expecting keyword_then or ',' or ';' or
'\n' (SyntaxError)
      when :first: find_first(options)
                  ^
/home/hemant/push_server/lib/db_connection.rb:59: syntax error,
unexpected keyword_when, expecting keyword_end
      when :all: find_all(options)
          ^
/home/hemant/push_server/lib/db_connection.rb:87: syntax error,
unexpected keyword_end, expecting $end
from /home/hemant/push_server/bin/boot.rb:34:in `<top (required)>'

However if i rewrite it like this, it works:

    def find(*args)
      options = args.extract_options!
      validate_find_options(options)
      case args.first
      when :first
        find_first(options)
      when :all
        find_all(options)
      else
        raise "Invalid find"
      end
    end

Why is this? Was this intended?

On Dec 21, 2007 12:14 PM, hemant kumar <gethemant@gmail.com> wrote:
> 62:    end
>
>
> Now, above case statement totally blows up with Ruby 1.9:

My test is with Ruby 1.8.6 but:

>
> /home/hemant/push_server/bin/boot.rb:34:in
> `require': /home/hemant/push_server/lib/db_connection.rb:58: syntax
> error, unexpected ':', expecting keyword_then or ',' or ';' or
> '\n' (SyntaxError)
>       when :first: find_first(options)

if you want to put the body of the when in the same line you need a
then keyword:

irb(main):018:0> def find(*args)
irb(main):019:1> case args.first
irb(main):020:2> when :first then puts "first"
irb(main):021:2> when :all then puts "all"
irb(main):022:2> else raise "invalid"
irb(main):023:2> end
irb(main):024:1> end
=> nil
irb(main):025:0> find :first, 1, 2, 3, 4
first
=> nil

>       else
>         raise "Invalid find"
>       end
>     end
>
> Why is this? Was this intended?

From the pickaxe:

"The then keyword (or a colon) separates the when comparisons from the
bodies and is
not needed if the body starts on a new line."

Hope this helps,

Jesus.

Jesús Gabriel y Galán wrote:
> if you want to put the body of the when in the same line you need a
> then keyword:

1.8.6 works with a keyword or a colon, I think this is what Hemant 
means.. 1.9 obviously doesn't support using them (I can't test it right 
now)

>> def find(*args)
>> case args.first
>> when :first: puts "first"
>> when :all: puts "all"
>> else raise "invalid"
>> end
>> end
=> nil
>> find :first, 1, 2, 3, 4
first


As you can see, Hemants example works fine with colons in 1.8.6, perhaps 
not in 1.9, though...

I normally use 'then' in either case..

Regards,
Lee

Jesús Gabriel y Galán wrote:
> if you want to put the body of the when in the same line you need a
> then keyword:

1.8.6 works with a keyword or a colon, I think this is what Hemant
means.. 1.9 obviously doesn't support using them (I can't test it right
now)

>> def find(*args)
>> case args.first
>> when :first: puts "first"
>> when :all: puts "all"
>> else raise "invalid"
>> end
>> end
=> nil
>> find :first, 1, 2, 3, 4
first


As you can see, Hemants example works fine with colons in 1.8.6, perhaps
not in 1.9, though...

I normally use 'then' in either case..

Regards,
Lee

On Dec 21, 2007 12:48 PM, Lee Jarvis <ljjarvis@gmail.com> wrote:
> >> when :first: puts "first"
> not in 1.9, though...
> I normally use 'then' in either case..

Oh, you are right, I missed the colon after the symbol. :-(
Sorry for the noise.

Jesus.

2007/12/21, hemant kumar <gethemant@gmail.com>:
> 62:    end
>       when :first: find_first(options)
>                   ^
> /home/hemant/push_server/lib/db_connection.rb:59: syntax error,
> unexpected keyword_when, expecting keyword_end
>       when :all: find_all(options)
>           ^
> /home/hemant/push_server/lib/db_connection.rb:87: syntax error,
> unexpected keyword_end, expecting $end
> from /home/hemant/push_server/bin/boot.rb:34:in `<top (required)>'

Does the same error surface if you precede the colon with a space?
Sorry, I don't have a 1.9 here to test this myself.

>       else
>         raise "Invalid find"
>       end
>     end
>
> Why is this? Was this intended?

Maybe the form with colon is deprecated?

Kind regards

robert

On Fri, 2007-12-21 at 21:01 +0900, Robert Klemme wrote:
> > 61:      end
> > '\n' (SyntaxError)
> Does the same error surface if you precede the colon with a space?
> >       when :all
> >         find_all(options)
> >       else
> >         raise "Invalid find"
> >       end
> >     end
> >
> > Why is this? Was this intended?
> 
> Maybe the form with colon is deprecated?
> 

Looks like they deprecated ":" in case statements.

Matz, shall we consider this as bug or change was unintentional?

On Fri, 2007-12-21 at 18:47 +0530, hemant kumar wrote:
> > > 60:      else raise "Invalid find"
> > > error, unexpected ':', expecting keyword_then or ',' or ';' or
> > 
> > >         find_first(options)
> > 
> 
> Looks like they deprecated ":" in case statements.
> 
> Matz, shall we consider this as bug or change was unintentional?

My bad.. i meant intentional, but you got the point anyways!.

Thanks

Le 21 décembre à 14:18, hemant kumar a écrit :

> My bad.. i meant intentional, but you got the point anyways!.

According to the 3rd edition of the PickAxe, it is intentional.

(p 125, Case Expressions : "Ruby 1.8 allowed you to use a colon
character in place of the then keyword. This is no longer supported.")

Fred

>> Looks like they deprecated ":" in case statements.
you can replace them with ";" or "then" to be Ruby 1.8 and 1.9
compatible. but it's ugly. I prefer the colon variant.

can we have the colon back, matz? at least for "case".
[murphy]

On Fri, 2007-12-21 at 22:55 +0900, F. Senault wrote:
> Le 21 décembre à 14:18, hemant kumar a écrit :
> 
> > My bad.. i meant intentional, but you got the point anyways!.
> 
> According to the 3rd edition of the PickAxe, it is intentional.
> 
> (p 125, Case Expressions : "Ruby 1.8 allowed you to use a colon
> character in place of the then keyword. This is no longer supported.")
> 

Ha ha.. damn to its decided. I don't own third edition apparently.

On Dec 21, 2007 9:01 AM, murphy <murphy@rubychan.de> wrote:
> >> Looks like they deprecated ":" in case statements.
> you can replace them with ";" or "then" to be Ruby 1.8 and 1.9
> compatible. but it's ugly. I prefer the colon variant.
>
> can we have the colon back, matz? at least for "case".
> [murphy]

I suspect that it's gone because of a conflict with the new keyword
style hash literal syntax in 1.9.

On the other hand changing the colon to a semi-colon will work.

   when :first; find_first(options)



--
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/