From: Jamis Buck <jgb3@...>
Date: 2003-12-06T01:21:42+09:00
Subject: Accessing the call stack

I've been wishing there were an easy to way to access Ruby's call
stack.  I mean, you can use "caller", but that just gives you an array
of strings.  Sometimes it would be nice to know the file, line, method
and object that invoked a particular method, without having to parse the
caller strings.  The object and/or class cannot even be obtained that
way.

Is there an easy way?  I wound up adding a trace function that
"listened" for call and return events, and then added them to a custom
stack.  This worked very well, but is not very robust since if anyone
sets a new trace function, the "call stack" is no longer accurate.

Here's my solution:

#-------------------------------------------------
def invoker
  Thread.current[:callstack] ||= []
  ( Thread.current[:callstack][-3] || Object )
end

set_trace_func proc { |event,file,line,obj,bind,klass|
  if event == "call"
    Thread.current[:callstack] ||= []
    Thread.current[:callstack].push klass
  elsif event == "return"
    Thread.current[:callstack].pop
  end
}
#-------------------------------------------------

All it tells you is the class of object that invoked the method, but it
could easily be extended.  What I really want to know is: have I
reinvented the wheel?  If not, perhaps something like this would be a
candidate for Rite...?

- Jamis