We recently had a problem where, after a series of commits had occurred, a backend process failed to run. Now, we were good little boys and girls and ran rake test
after every check-in but, due to some oddities in Rails' library loading, it only occurred when we ran it directly from Mongrel in production mode.
I tracked the bug down and it was due to a new Rails gem overwriting a method in the String class in a way that broke one narrow use in the runtime Rails code.
Anyway, long story short, is there a way, at runtime, to ask Ruby where a method has been defined? Something like whereami( :foo )
that returns /path/to/some/file.rb line #45
? In this case, telling me that it was defined in class String would be unhelpful, because it was overloaded by some library.
I cannot guarantee the source lives in my project, so grepping for 'def foo'
won't necessarily give me what I need, not to mention if I have many def foo
's, sometimes I don't know until runtime which one I may be using.
This is really late, but here's how you can find where a method is defined:
# How to find out where a method comes from.
# Learned this from Dave Thomas while teaching Advanced Ruby Studio
# Makes the case for separating method definitions into
# modules, especially when enhancing built-in classes.
module Perpetrator
def crime
end
end
class Fixnum
include Perpetrator
end
p 2.method(:crime) # The "2" here is an instance of Fixnum.
#<Method: Fixnum(Perpetrator)#crime>
If you're on Ruby 1.9+, you can use source_location
require 'csv'
p CSV.new('string').method(:flock)
# => #<Method: CSV#flock>
CSV.new('string').method(:flock).source_location
# => ["/path/to/ruby/1.9.2-p290/lib/ruby/1.9.1/forwardable.rb", 180]
Note that this won't work on everything, like native compiled code. The Method class has some neat functions, too, like Method#owner which returns the file where the method is defined.
EDIT: Also see the __file__
and __line__
and notes for REE in the other answer, they're handy too. -- wg