This allows you to skip callbacks that are defined by objects, e.g. for
`ActionController`:
skip_after_filter MySpecialFilter
Previously this didn't work due to a bug in how Rails compared callbacks
in `Callback#matches?`. When a callback is compiled, if it's an object
filter (i.e. not a method, proc, etc.), `Callback` now defines a method on
`@klass` that is derived from the class name rather than `@callback_id`.
So, when `skip_callback` tries to find the appropriate callback to
remove, `Callback` can regenerate the method name for the filter
object and return the correct value for `Callback#matches?`.
When you add one callack in two separate `set_callback` calls - it is
only called once.
When you do it in one `set_callback` call - it is called twice.
This violates the principle of least astonishment for me. Duplicating
callback is usually an error. There is a correct and obvious way to do
anything without this "feature".
If you want to do
before_save :clear_balance, :calculate_tax, :clear_balance
or whatever, you should better do
before_save :carefully_calculate_tax
def carefully_calculate_tax
clear_balance
calculate_tax
clear_balance
end
And this even opens gates for some advanced refactorings, unlike the
first approach.
My assumptions are:
- Principle of least astonishment is violated, when callbacks are either
prevented from duplication, or not.
- Duplicating callbacks is usually an error. When it is intentional -
it's a smell of a bad design and can be approached without abusing
this "feature".
My suggestion is: do not allow duplicating callbacks in one callback
call, like it is not allowed in separate callbacks call.
no test was failing. Tests have been added to ensure that commenting
out the code within if loop would cause test failure.
Signed-off-by: José Valim <jose.valim@gmail.com>