From: mortee <mortee.lists@...>
Date: 2007-10-12T08:59:41+09:00
Subject: Re: Using strings to drill down into objects

Ross X Dawson wrote:
> Sorry folks the example was not correct
> 
> irb(main):001:0> drill_down = lambda do |obj, method_names|
> irb(main):002:1*        o ||= obj
> irb(main):003:1>        method_names.split('.').each {|m| o = o.send(m)}
> irb(main):004:1>        o
> irb(main):005:1> end
> => #<Proc:0x40221e48@(irb):1>
> irb(main):006:0> drill_down.call(1,'succ.to_s')
> => "2"
> irb(main):007:0> drill_down.call(1,'succ.succ.succ.to_s')
> => "4"
> irb(main):008:0>
> 
> This is what I currently have working.  I'm using it to define the columns
> in a report so I need to determine the result of arbitrary fields within
> the object model.  I just look at the code and think there is a better way.

OK, that makes more sense. Still, we don't know what you have to start
with (I guess it's not simply 1 :), and how much flexibility you need in
accessing various things about that thing.

For example, do you really need a lambda as your "drill down" function?
One might think if it's so flexible, a simple method would suffice.

Also, are you sure you have to traverse an object hierarchy by following
arbitrarily specifiable attribute accessors in turn? It seems quite
weird for a data model.

Finally, given that you already use lambdas, you could just use those to
specify the way to access what you're looking for, starting from a given
object.

Just to keep some resemblance to your code (it could be made even simpler):

def drill_down(obj, func)
	yield.call(obj)
end

drill_down(1, lambda{|o| o.succ.to_s})			#=> "2"
drill_down(1, lambda{|o| o.succ.succ.succ.to_s})	#=> "4"

And then you can simply use code blocks passed to the method call:

def drill_down(obj)
	yield obj
end

drill_down(1) {|o| o.succ.to_s}			#=> "2"
drill_down(1) {|o| o.succ.succ.succ.to_s}	#=> "4"

If the method which calls drill_down receives the lambdas in question as
parameters, you can still pass them on as code blocks:

some_lambda = lambda{|o| o.succ.to_s}
drill_down(1, &some_lambda)			#=> "2"

mortee