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alias method by Ruby

Sometimes, you want to inject some logic before or after a method invocation. Right, this is one of the typical usage of aspect programming in Java.

But in dynamic language such as Ruby or Python, the language allows you to do this without using any aspect oriented language or tool.

Here is a ruby version, which demonstrates to inject trace message on invocation of  methods specified. I also shows the Python version here.

#!/usr/bin/env ruby -w

class Module
    private
    def trace_it(*ids)
      for id in ids
        module_eval <<-"end;"
          alias_method :__#{id.to_i}__, :#{id.to_s}
          private :__#{id.to_i}__
          def #{id.to_s}(*args, &block)
            puts "[#{Time.now.asctime}] #{name} #{id.to_s} started"
            retval = __#{id.to_i}__(*args, &block)
            puts "[#{Time.now.asctime}] #{name} #{id.to_s} finished"
            return retval
          end
        end;
      end   
    end
end

class Test1
  def foo1()
    puts "foo1()"
  end

  def foo2()
    puts "foo2()"
  end
end

class Test1
  trace_it :foo1, :foo2
end

t1 = Test1.new()
t1.foo2
t1.foo1

alias method by Python

This is the python version of ruby alias_method equivalent.

#!/usr/bin/env python
from datetime import *

def trace_it(method):
    # retrieve the enclosing class of the method
    class_ = method.im_class
    # retrieve the method name
    name_ = method.__name__

    def alias_method(*args, **kwargs):
        print "[%s] %s %s srated" % (datetime.today(), class_.__name__, name_)
        retval = method(*args, **kwargs)
        print "[%s] %s %s finished" % (datetime.today(), class_.__name__, name_)
        return retval

    # replace the original method with the alias
    setattr(class_, name_, alias_method)

class Test1(object):
    def foo1(self):
        print 'foo1()'

    def foo2(self):
        print 'foo2()'

trace_it(Test1.foo1)

tc = Test1()
tc.foo1()
tc.foo2()