From: Paul Brannan <pbrannan@...>
Date: 2002-12-08T01:46:19+09:00
Subject: Re: [RCR] Accessor for trace_func

I think this proposed RCR is a good idea.  It allows trace funcs to be
chained together, which is a good thing if you want to trace and profile
at the same time.

It might be nice if the RCR requested that $trace_func be a hooked
global variable.

One problem with chaining trace funcs is that it makes it difficult to
remove a trace func from the chain.  Another solution, if you don't want
to wait for Ruby to change, is to redefine set_trace_func:

  $trace_funcs = []

  class Object
    alias_method :old_set_trace_func, :set_trace_func

    def set_trace_func(func)
      $trace_funcs.push(func)
    end

    old_set_trace_func proc { |*args|
      $trace_funcs.each { |f| f.call(*args) }
    }
  end

Any call to set_trace_func will now add the func to the list of trace
funcs instead of replacing the existing one.  This makes it easy to
remove a trace func (just write a remove_trace_func method), but will
have the side effect of breaking code that relies on "set_trace_func
nil" removing all existing trace funcs.

Paul