Cheap Tricks IX - Spying on Ruby

St. Louis was fun. They have a very active Java user community and met loads of nice folks. Other than that, not much new or exciting today. Crashed on a friend's couch last night so brain not function so good.

But... here is some fun Ruby-spying techniques to help round out the week. The first one attaches a trace to "require" and prints out the file and line that is making the first call to "require":
# Trace who loads what first<br />alias _require require<br />def require(*args)<br /> puts "Loading #{args[0]} in #{caller.shift}"<br /> _require(*args)<br />end
Here is a way to trace every line that creates a new object.
# Trace who creates what objects where<br />class Class<br /> alias _new new<br /> def new(*args, &block)<br /> puts "New #{self.name} in #{caller.shift}"<br /> _new(*args, &block)<br /> end<br />end
A little more generalized, here we trace calls to specific methods for a given class that "requests" to be traced:
# Trace called methods<br />class Module<br /> def attach_traces<br /> methods.each do |m|<br /> attach_method_trace(m) unless m.to_s == 'class' or m.to_s == 'caller'<br /> end<br /> end<br /><br /> def attach_method_trace(m_sym)<br /> method = instance_method(m_sym)<br /> define_method(m_sym) do |*args|<br /> puts "Calling #{self.class.name}.#{m_sym} in #{caller.shift}"<br /> method.bind(self).call(*args) <br /> end<br /> rescue NameError<br /> end<br />end
And here is how any class can request it's methods be traced:
String.attach_traces
Finally, you can add a little extra zing by cleaning up the output of the "caller.shift" file location like so:
# Trace who loads what first<br />alias _require require<br />def require(*args)<br /> s = caller.shift<br /> $:.each {|b| puts("Loading #{args[0]} in #{s}") || break if s.sub!(%r"^#{b}/?", '')}<br /> _require(*args)<br />end<br />