an oop question

[Julieta Shem]

Chris Angelico <rosuav at gmail.com> writes:

> On Mon, 31 Oct 2022 at 09:05, Julieta Shem <jshem at yaxenu.org> wrote:
>>
>> Julieta Shem <jshem at yaxenu.org> writes:
>>
>> [...]
>>
>> >>   . If you should, however, be talking about the new "type hints":
>> >>   These are static and have "Union", for example, "Union[int, str]"
>> >>   or "int | str".
>> >
>> > I ended up locating such features of the language in the documentation,
>> > but I actually am not interested in declaring the type to the compiler
>> > (or to the reader).
>> >
>> > I was looking for a solution like yours --- thank you! ---, although I
>> > was hoping for handling that situation in the construction of the Stack
>> > object, which was probably why I did not find a way out.  Right now I'm
>> > looking into __new__() to see if it can somehow produce one type or
>> > another type of object depending on how the user has invoked the class
>> > object.
>> >
>> > Terminology.  By ``invoking the class object'' I mean expressions such
>> > as Class1() or Class2().  ``Class1'' represents the object that
>> > represents the class 1.  Since the syntax is that of procedure
>> > invokation, I say ``invoking the class object''.
>>
>> An experiment.  What's my definition of Stack?  It's either Empty or
>> Pair, so it's a union.  So let us create two inner classes (that is,
>> inner to Stack) and make them behave just like Empty and Pair.  Using
>> __new__(), we can produce a Stack object that is sometimes Empty() and
>> sometimes Pair(...).
>>
>
> The most straight-forward way to represent this concept in an
> object-oriented way is subclassing.
>
> class Stack:
>     ... # put whatever code is common here
>
> class Empty(Stack):
>     ... # put Empty-specific code here, possibly overriding Stack methods
>
> class Pair(Stack):
>    ... # ditto, overriding or augmenting as needed
>
> This way, everything is an instance of Stack, but they are still
> distinct types for when you need to distinguish.

Can you provide a small example?  I can't see what you mean, but it
seems interesting.