SafeMonkeypatch

If you can, please, DO NOT monkeypatch.

Sometimes I patch ActiveRecord, but ain't sure if it's gonna break in the next version of Rails. This gem would raise an error if monkey patched method has changed since last time you've adapted your patch to the upstream.

Usage

# assume some upstream in foo.gem:
class Foo
  def bar
    puts "do first thing"
    puts "do second thing"
    puts "do something else"
  end
end

# your code
class Foo

  # you can use any of Digest::*** checksum's methods: sha1, etc.
  # NOTE: do this BEFORE monkeypatch happens
  safe_monkeypatch :bar, md5: "", error: "my additional info for exception"

  def bar
    puts "do first thing"
    # puts "do second thing" # don't do that
    puts "do something else"
  end
end

Until upstream code isn't changed, it's working like usual. But if the new version changes the implementation of Foo#bar method, an error is raised while startup time (unless you monkeypatch in runtime, but now you're on your own):

SafeMonkeypatch::UpstreamChanged: Foo#bar expected to have md5 checksum: "", but has: ""
my additional info for exception

You can also use it without patched module scope (for proper error use patched class/module name):

Foo.safe_monkeypatch Foo.instance_method(:bar), md5: 'invalid_checksum'

Happy monkeypatching :)