Problem with case statements


H

hemant kumar

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?
 
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J

Jesús Gabriel y Galán

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:

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
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?

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.
 
L

Lee Jarvis

Jesús Gabriel y Galán said:
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)
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
 
L

Lee Jarvis

Jesús Gabriel y Galán said:
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)
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
 
J

Jesús Gabriel y Galán

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)

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..

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

Jesus.
 
R

Robert Klemme

2007/12/21 said:
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)>'

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.
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?

Maybe the form with colon is deprecated?

Kind regards

robert
 
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H

hemant kumar

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.


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?
 
H

hemant kumar

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
 
F

F. Senault

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
 
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H

hemant kumar

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


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.
 

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