Weird behavior of case/when

ruby-talk
1

I'm getting a very weird result using case/when.

$ cat test.rb
def test(a)
  case a.class
  when Class
    puts "class"
  when String
    puts "string"
  else
    puts "else"
  end
end

test(Float)
test("hello")
test(42)
$ ruby test.rb
class
$ ruby --version
ruby 1.8.4 (2005-12-24) [i686-linux]

I would have exepected the following output:

class
string
else

Does anyone have an explanation about this issue?

Cheers,

···

--
Nicolas Desprès

2

case uses === which is well defined for obj === class.
What you do is checking the class of a.class which is a class itself.

To make it short: use 'case a' instead of 'case a.class'

cheers

Simon

···

-----Original Message-----
From: Nicolas Desprès [mailto:nicolas.despres@gmail.com]
Sent: Wednesday, July 12, 2006 10:31 AM
To: ruby-talk ML
Subject: Weird behavior of case/when

I'm getting a very weird result using case/when.

$ cat test.rb
def test(a)
  case a.class
  when Class
    puts "class"
  when String
    puts "string"
  else
    puts "else"
  end
end

test(Float)
test("hello")
test(42)
$ ruby test.rb
class
class
class
$ ruby --version
ruby 1.8.4 (2005-12-24) [i686-linux]

I would have exepected the following output:

class
string
else

Does anyone have an explanation about this issue?

Cheers,

3

Nicolas Desprès schrieb:

I'm getting a very weird result using case/when.
(...)

Nicolas, why do you find it weird? Have you read the documentation, for example

   Expressions

Regards,
Pit

4

Thank you. I knew that case uses === but I would have never expected
that it behaves this way.

Regards,

···

On 7/12/06, Kroeger, Simon (ext) <simon.kroeger.ext@siemens.com> wrote:

case uses === which is well defined for obj === class.
What you do is checking the class of a.class which is a class itself.

To make it short: use 'case a' instead of 'case a.class'

--
Nicolas Desprès

5

Nicolas Desprès wrote:

···

On 7/12/06, Kroeger, Simon (ext) <simon.kroeger.ext@siemens.com> wrote:

case uses === which is well defined for obj === class.
What you do is checking the class of a.class which is a class itself.

To make it short: use 'case a' instead of 'case a.class'

Thank you. I knew that case uses === but I would have never expected
that it behaves this way.

Regards,

It should behave that in a language where classes are objects :smiley: (unlike java where instances of java.lang.Class are just proxies to vm internals)

lopex