On 2021-06-20 7:48 p.m., Steven D'Aprano wrote:
> The technique you are calling "extension methods" is known as
> "monkey-patching" in Python and Ruby.
>
> With respect to a fine language, Kotlin, it doesn't have the user-base
> of either Python or Ruby. Python does not allow monkey-patching builtin
> classes, but Ruby does:
>
> https://avdi.codes/why-monkeypatching-is-destroying-ruby/
>
> A cautionary tale. So what does Kotlin do to prevent that sort of thing?
>
> Can you use a regular function that takes a list as argument, instead of
> monkey-patching the list class to add a method?
>
> The beauty of a function is that every module is independent, so they
> can add their own list extensions (as functions) without stomping over
> each other. Whereas if they add them directly on to the list class
> itself, they can clash.
>
The trick to extension methods is that they're only available when you
explicitly use them.
In other words, a module/package can't force them on you.
The problem with "monkey-patching" is that it *does* get forced on you.
With the way Python works, your only option to implement extension
methods is to monkey-patch __getattr__. An alternative would be to have
a module-level __getattr__, which by default resolves to the object's
own attributes, but can be replaced by the module to provide proper
(module-local) extension methods functionality. Thus, any module-local
extension methods would also take priority over subclasses' attributes,
without conflicting with them.
(It would also slow everything down af, but that's beside the point.)
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