From: Hal Fulton <hal9000@...>
Date: 2004-07-17T05:21:17+09:00
Subject: Dynamically replacing methods for efficiency

I have an idea here, but I'm afraid of crossing the line from
cleverness to madness.

Imagine you have a class with methods whose behavior changes
based on various attributes.

For example, I'll name this method "action"; suppose that in
general, it just calls do_this and do_that.

   def action
     do_this
     do_that
   end

But now suppose we enable things like a debug mode and a
trace mode and logging and a configurable delay and such:

   def action
     STDERR.puts "Entering action" if @trace
     STDERR.puts "before do_this: foo = #@foo" if @debug
     @log.puts "#{Time.now}: Useful info" if @log
     sleep(@delay) if @delay
     do_this
     STDERR.puts "Returned from do_this" if @trace
     STDERR.puts "after do_this: foo = #@foo" if @debug
     @log.puts "#{Time.now}: More useful info" if @log
     do_that
     STDERR.puts "Returned from do_that" if @trace
     STDERR.puts "after do_that: foo = #@foo" if @debug
     @log.puts "#{Time.now}: Still more useful info" if @log
   end

Here we've added ten if-statements. If #action is called
frequently, performance will degrade even if these special
attributes are not set.

But suppose for example we fixed the "trace" setter so that
when it was set, it aliased "action_trace" to "action",
where the former is something like:

   def action_trace
     STDERR.puts "Entering action"
     do_this
     STDERR.puts "Returned from do_this"
     do_that
     STDERR.puts "Returned from do_that"
   end

There would also be versions like: action_log, action_debug,
not to mention (here's where it gets hairy) things like
action_debug_log, action_debug_trace, action_debug_trace_log,
and so on.

On the one hand, I appreciate Ruby because I *can* do this
sort of thing. On the other hand, if the logic for #action
changes, how many pieces of code will I find myself modifying?

Another possibility is: When a special attribute is changed,
write the method code to a file and load that file. This at
least would keep all the logic in one place.

Please: Express your opinions.


Hal