Forum: Ruby on Rails "obj.is_one_of? {Class1, Class2, ...}" as similar to "obj.is_a?(Class1) or obj.is_a?(Class2)"

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Jm F. (Guest)
on 2009-01-16 19:22
(Received via mailing list)
I need to check if a given object is an instance of a range of
Classes, and I was wondering if I could do it by passing in is_a? an
hash of classes, instead of calling is_a? for each class I have to
compare...
As I state in the subject (obj.is_one_of? {Class1, Class2, ...}), this
could justify a method "obj.is_one_of?" which returns true if the
object "obj" is an instance of Class1 or Class2...
Is there something that I'm missing?
Rob B. (Guest)
on 2009-01-16 19:40
(Received via mailing list)
On Jan 16, 2009, at 12:21 PM, jmfreitas wrote:
> I need to check if a given object is an instance of a range of
> Classes,

Are you sure?  It would be more idiomatic to check for duck-typing:
  obj.respond_to? :my_method
or to just call it and deal with the consequences:
  begin
    obj.my_method
  rescue NoMethodError
    # deal with it
  end

You already have something similar with:
  case obj
  when Class1, Class2
    # Yippee!
  else
    # Drat!
  end


> and I was wondering if I could do it by passing in is_a? an
> hash of classes, instead of calling is_a? for each class I have to
> compare...
> As I state in the subject (obj.is_one_of? {Class1, Class2, ...}), this
> could justify a method "obj.is_one_of?" which returns true if the
> object "obj" is an instance of Class1 or Class2...
> Is there something that I'm missing?

What are you trying to do that causes you to want this?

-Rob

Rob B.    http://agileconsultingllc.com
removed_email_address@domain.invalid
Jm F. (Guest)
on 2009-01-16 20:36
(Received via mailing list)
Thanks so much for the quick and useful reply...
The suggestion to use "case obj when Class1, Class2" completely
fulfills my needs, most appreciated :-D
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