Detecting when an instance variable is created/set

ruby-talk
21

Hi –

Unfortunately, for it to be useful to me, I’d specifically need it to
work in initialize() as well.

I don’t know why it does not work in initialize (I assumed it would).
A dirty fix:

module Initializer
def initialize(*args)
puts “Here I’ll handle these variables: #{instance_variables.inspect}”
end
end

module MonitorVariables
…
end

class Test
def initialize(*args)
@a = 1
@b = ‘world’
super(*args)
end

What is that super() calling? It seems to be the initialize() in Initializer,
but I don’t understand why. I would have thought that it would be calling
the one from perhaps Object (since Test doesn’t specifically subclass
anything else).

I also don’t know why, if put in MonitorVariables, initialize won’t be
called, and needs to be put in a different module.

I added the code in your Initializer module into MonitorVariables and it
worked OK, so while it seems initialize() seems to need to be handled
separately, it doesn’t appear to need to be in a different module.

My experience was the same as Massimiliano’s: the #initialize didn’t
seem to get found by ‘super’ if it was in the same module as
#append_features. I don’t know why not.

(On #initialize being handled separately – see earlier post about
private methods.)

I still have the issue, though, that with this module included, all of the
instance variables end up being set to “true”, rather than to the values they
were actually assigned.

Any idea why that is and how to fix it?

Yes – the dynamically created replacement methods in M.'s
append_features method aren’t returning the value of the call to the
original method. Here’s what I think is a drop-in replacement (a few
variable names tweaked just to conform to my habits while hacking :slight_smile:

module MonitorVariables
def self.append_features(klass)
(klass.instance_methods + [‘initialize’]).each do |method|
oldmeth = “___#{method}”
klass.class_eval <<-EOF
alias #{oldmeth} #{method}
def #{method}(*params,&block)
old_iv = instance_variables
res = #{oldmeth}(*params,&block)
(diff = instance_variables - old_iv).empty? or
puts “variable(s) " + diff.inspect +
" added in method #{method}”
return res
end
EOF
end
end
end

I’m wondering, though, whether there’s a simpler way to do what you’re
trying to do (the self.a = x approach maybe?).

David

···

On Mon, 5 Aug 2002, Harry Ohlsen wrote:

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

22

I also don’t know why, if put in MonitorVariables, initialize won’t be
called, and needs to be put in a different module.

I added the code in your Initializer module into MonitorVariables and it
worked OK, so while it seems initialize() seems to need to be handled
separately, it doesn’t appear to need to be in a different module.

Uhm, did it work for you? Could you post the code?

I still have the issue, though, that with this module included, all of the
instance variables end up being set to “true”, rather than to the values they
were actually assigned.

Any idea why that is and how to fix it?

As David pointed out, the code was not saving the return value of the
__method and was returning the return value of puts “variables …”
etc.

Massimiliano

···

On Mon, Aug 05, 2002 at 06:19:20AM +0900, Harry Ohlsen wrote: