Monkey-patching Vs. S.O.L.I.D. principles?

Question

I\'m slowly moving from PHP5 to Python on some personal projects, and I\'m currently loving the experience. Before choosing to go down the Python route I looked at Ruby. Wha

Answer 1

In my view, monkeypatching is useful to have but something that can be abused. People tend to discover it and feel like it should be used in every situation, where perhaps a mixin or other construct may be more appropriate.

I don't think it's something that you should outlaw, it's just something that the Ruby guys like to use. You can do similar things with Python but the community has taken the stance that things should be simpler and more obvious.

Answer 2

There's a difference between monkey-patching (overwriting or modifying pre-existing methods) and simple addition of new methods. I think the latter is perfectly fine, and the former should be looked at suspiciously, but I'm still in favour of keeping it.

I've encountered quite a few those problems where a third party extension monkeypatches the core libraries and breaks things, and they really do suck. Unfortunately, they all invariably seem stem from the the third party extension developers taking the path of least resistance, rather than thinking about how to actually build their solutions properly.
This sucks, but it's no more the fault of monkey patching than it's the fault of knife makers that people sometimes cut themselves.

The only times I've ever seen legitimate need for monkey patching is to work around bugs in third party or core libraries. For this alone, it's priceless, and I really would be disappointed if they removed the ability to do it.

Timeline of a bug in a C# program we had:

1. Read strange bug reports and trace problem to a minor bug in a CLR library.
2. Invest days coming up with a workaround involving catching exceptions in strange places and lots of hacks which compromises the code a lot
3. Spend days extricating hacky workaround when Microsoft release a service pack

Timeline of a bug in a rails program we had:

1. Read strange bug reports and trace problem to a minor bug in a ruby standard library
2. Spend 15 minutes performing minor monkey-patch to remove bug from ruby library, and place guards around it to trip if it's run on the wrong version of ruby.
3. Carry on with normal coding.
4. Simply delete monkeypatch later when next version of ruby is released.

The bugfixing process looks similar, except with monkeypatching, it's a 15 minute solution, and a 5-second 'extraction' whereas without it, pain and suffering ensues.

PS: The following example is "technically" monkeypatching, but is it "morally" monkeypatching? I'm not changing any behaviour - this is more or less just doing AOP in ruby...

class SomeClass
  alias original_dostuff dostuff
  def dostuff
    # extra stuff, eg logging, opening a transaction, etc
    original_dostuff
  end
end