Reflection for instance variables?

ruby-talk
1

Hi. I’m brand new to Ruby, so please pardon if this question is naive,
but I have not been able to figure it out. I would like to come up with
a way to define a method in a superclass that would give me a list of
variables in a subclass. So:

class Father
@h_test = “1234”
@h_test2 = “12345”

def Father.vars
return self.instance_vars # This does not work.
end
end

class Son < Father
@h_test3 = "123456"
end

print Son::vars

end listing

Would give me [‘h_test’, ‘h_test2’, ‘h_test3’]. It seems to me that
the key would be to get a reference to the Class object for the
subclass, but can’t seem to figure out how to do that. Suggestions?

(For the curious, I’m trying to do something in Ruby I saw in
objective-c. This class allowed you to define a subclass, define the
variables in the subclass, then it would create the sql, etc.
automagically.)

Thanks,

Patrick

2

Hi. I’m brand new to Ruby, so please pardon if this question is naive,
but I have not been able to figure it out. I would like to come up with
a way to define a method in a superclass that would give me a list of
variables in a subclass. So:

dont think a class method is going to cut it, for a couple of reasons.

but perhaps this:

class Father
@h_test = “1234”
@h_test2 = “12345”
def vars
return self.instance_vars - self.superclass.instance_vars
end
end

class Son < Father
@h_test3 = “123456”
end

s = Son.new
print s.vars

NOT TESTED!!!

(For the curious, I’m trying to do something in Ruby I saw in
objective-c. This class allowed you to define a subclass, define the
variables in the subclass, then it would create the sql, etc.
automagically.)

sounds fun! and good luck.

···

On Saturday 25 January 2003 08:34 pm, Patrick Narkinsky wrote:

–
tom sawyer, aka transami
transami@transami.net

3

Hi –

Hi. I’m brand new to Ruby, so please pardon if this question is naive,

Welcome to Ruby!

but I have not been able to figure it out. I would like to come up with
a way to define a method in a superclass that would give me a list of
variables in a subclass. So:

class Father
@h_test = “1234”
@h_test2 = “12345”

def Father.vars
return self.instance_vars # This does not work.

I think you mean “instance_variables”.

end
end

class Son < Father
@h_test3 = “123456”
end

print Son::vars

end listing

Would give me [‘h_test’, ‘h_test2’, ‘h_test3’]. It seems to me that
the key would be to get a reference to the Class object for the
subclass, but can’t seem to figure out how to do that. Suggestions?

I’m not 100% sure what you mean, but let me try something which
probably isn’t what you mean, and maybe you can bridge the gap or
bounce it back:

class Father
def self.report_ivs
ancestors.map {|a| a.instance_variables}.flatten.compact
end
@x = 1
@y = 2
end

class Son < Father
@z = 3
end

p Father.report_ivs # [“@y”, “@x”]
p Son.report_ivs # [“@z”, “@y”, “@x”]

David

···

On Sun, 26 Jan 2003, Patrick Narkinsky wrote:

–
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web: http://pirate.shu.edu/~blackdav

4

thanks - that’s exactly what I was looking for. In retrospect, I
suppose it was naive to expect Ruby to story the instance variables for
all inherited classes in one place.

Patrick

···

On Sunday, January 26, 2003, at 12:46 AM, dblack@candle.superlink.net wrote:

I’m not 100% sure what you mean, but let me try something which
probably isn’t what you mean, and maybe you can bridge the gap or
bounce it back: