Basic question about Ruby's class hierarchy

[Patrick Li]

Hi,
I thought I understood this, but apparently not.

What is this object exactly?
o = class << String; self; end

From my understanding:
p o
and
p String
should output the same thing.

but it doesn't
p o #<Class:String>
p String #String

Thanks for answering such a basic question for me.
-Patrick

 

[Eric I.]

I thought I understood this, but apparently not.

What is this object exactly?
o = class << String; self; end

From my understanding:
p o
and
p String
should output the same thing.

but it doesn't
p o #<Class:String>
p String #String

o is not the same as String. o is String's metaclass. The exact role
that metaclasses play is Ruby's take on object-oriented programming is
too much for an answer post such as this. But you might want to read
why's explanation at:

http://www.whytheluckystiff.net/articles/seeingMetaclassesClearly.html

Eric

====

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On-site and customized training are available.

 

[Chris Shea]

Hi,
I thought I understood this, but apparently not.

What is this object exactly?
o = class << String; self; end

From my understanding:
p o
and
p String
should output the same thing.

but it doesn't
p o #<Class:String>
p String #String

Thanks for answering such a basic question for me.
  -Patrick

In your example, String is an instance of Class, and o is the
eigenclass (or metaclass) of String. Maybe this will help clarify:

o = class << String; self; end
o.class_eval do
def backwards
'gnirtS'
end
end

String.backwards # => "gnirtS"

HTH,
Chris