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From: Tomasz Wrobel on 6 Aug 2010 04:57
Hi!

Do you know a good way to check whether a class is a subclass of a
certain class (given the class object, not an instance)?

one way would be to check all of klass.superclass,
klass.superclass.superclass till nil

or klass.new.is_a?( cklass )

Accidentaly, I tried to such a operation:

klass < cklass

and it seems to work, but doesn't seem to be documented
can somebody acknowledge this?

Best regards,
Tomek W
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From: Jesús Gabriel y Galán on 6 Aug 2010 05:15
On Fri, Aug 6, 2010 at 10:57 AM, Tomasz Wrobel <tomekwr(a)gmail.com> wrote:
> Hi!
>
> Do you know a good way to check whether a class is a subclass of a
> certain class (given the class object, not an instance)?
>
> one way would be to check all of klass.superclass,
> klass.superclass.superclass till nil
>
> or klass.new.is_a?( cklass )

Klass.ancestors.include?(Ancestor)

For example:

irb(main):003:0> String.ancestors.include? Object
=> true

Jesus.

From: Quintus on 6 Aug 2010 05:25
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Am 06.08.2010 10:57, schrieb Tomasz Wrobel:
> Hi!
>
> Do you know a good way to check whether a class is a subclass of a
> certain class (given the class object, not an instance)?
>
> one way would be to check all of klass.superclass,
> klass.superclass.superclass till nil
>
> or klass.new.is_a?( cklass )
>
> Accidentaly, I tried to such a operation:
>
> klass < cklass
>
> and it seems to work, but doesn't seem to be documented
> can somebody acknowledge this?
>
> Best regards,
> Tomek W


It is documented, although it may be a bit hard to find, since the
behaviour is not defined in the Class class as one might expect, but in
it's superclass, Module. See the Module#<, Module#>, Module#<= and
Module#>= methods on http://www.ruby-doc.org/ruby-1.9/index.html . I'm
not sure what about Module#<=> since the docs say it works on mixins,
but it appears to work on classes as well.

Vale,
Marvin
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From: Tomasz Wrobel on 6 Aug 2010 06:49
> It is documented, although it may be a bit hard to find, since the

I see. I got deceived by the fact that the method actually seems to be
defined in Object.

Thanks for answers,
best regards,
Tomek W
--
Posted via http://www.ruby-forum.com/.

From: Michał Łomnicki on 6 Aug 2010 06:53

> It is documented, although it may be a bit hard to find, since the
> behaviour is not defined in the Class class as one might expect, but in
> it's superclass, Module.

What's more '<' operator itself is defined in Object class not in
Module.

> Module.methods - Object.methods
=> ["nesting"]

So all in all one expects '<' method to be defined for Class, but it's
defined for Object and documented for Module. Pretty messy ;)
--
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