Is subclass known in superclass.initialize? (virtual constructor theme...)

ruby-talk
1

Is there a reasonable replacement for ‘?’ below?

class Super
    def initialize
        sub = '?'    # something that yields obj.class
        puts "Created for subclass #{sub}"
    end
end

class Sub < Super
end

obj = Sub.new

Thanks,
Sab

2

“Szabolcs Szasz” sz@szasz.hu writes:

Is there a reasonable replacement for ‘?’ below?

class Super
    def initialize
        sub = '?'    # something that yields obj.class
        puts "Created for subclass #{sub}"
    end
end

‘type’ returns the class of its receiver, so:

class Super
def initialize
sub = type
puts “Created for subclass #{sub}”
end
end

class Sub < Super
end

obj = Super.new #=> Created for subclass Super
obj = Sub.new #=> Created for subclass Sub

So can also use #class, but you have to be careful to call it with an
explicit receiver, or Ruby will think you’re starting a class
definition.

Cheers

Dave

3

I did start with the class/type method, but still only saw the
superclass in the constructor… Strange, I must have missed
something subtle in the actual code (which is different from
my gutted example below).

Needless to say, now it does work just fine in the original
code, too…

Well, it can be a bit frustrating to be a newbie sometimes… :wink:

Thanks very much,
Sab

···

----- Original Message -----
From: “Dave Thomas” Dave@PragmaticProgrammer.com
To: “ruby-talk ML” ruby-talk@ruby-lang.org
Sent: Sunday, October 20, 2002 4:07 AM
Subject: Re: Is subclass known in superclass.initialize? (virtual constructor theme…)

“Szabolcs Szasz” sz@szasz.hu writes:

Is there a reasonable replacement for ‘?’ below?

class Super
    def initialize
        sub = '?'    # something that yields obj.class
        puts "Created for subclass #{sub}"
    end
end

‘type’ returns the class of its receiver, so:

class Super
def initialize
sub = type
puts “Created for subclass #{sub}”
end
end

class Sub < Super
end

obj = Super.new #=> Created for subclass Super
obj = Sub.new #=> Created for subclass Sub

So can also use #class, but you have to be careful to call it with an
explicit receiver, or Ruby will think you’re starting a class
definition.

Cheers

Dave

4

‘type’ returns the class of its receiver, so:
(snip)
So can also use #class, but you have to be careful to call it with an
explicit receiver, or Ruby will think you’re starting a class
definition.

Object#type is being deprecated in the development version (though I
don’t know why), so I’d recommend “self.class”.

···

At Sun, 20 Oct 2002 11:07:51 +0900, Dave Thomas wrote:

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