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Archive for March 18th, 2011

Temporary overwrite method for specific task

March 18th, 2011 by

today I must solve issue with not well structured code. Problem is that one method return last correct version, but in one specific case it needs to return newest version (even incorrect). There is many calls between top level method which know what needs to call and target method which is called from generic code. Now I need to fix it and code is not well tested and quite sensitive to changes ( this fix is fix of another fix :). So what is the safest way to change it?
I decide that the best solution which doesn’t change almost nothing ( but is suitable just for maintenance update, for trunk I create better solution ) is temporary overwrite of target method to change its behavior. Now how to do it?
There is simple example:

class T
  def test
    puts "test"

  def lest
    puts "lest"

  def m

T.send(:define_method,:m_a) { lest }
T.send(:alias_method, :m_old, :m)
T.send(:alias_method, :m, :m_a)
T.send(:alias_method, :m, :m_old)
T.send(:undef_method, :m_a)
T.send(:undef_method, :m_old)

as you can see after modification class is exact same as before ( except if there is method a, but it is possible to handle it via introspection and dynamic choose of method). I don’t need to change whole stack of calls to add parameter or introduce new singleton class which can have flag.
I hope it help someone with his fix of not so well written piece of software.