Pattern, Abstract Factory / Factory

[Marco Antoniotti]

... and I can always CHANGE-CLASS, can't I?

On Sun, Feb 7, 2021 at 9:46 AM Hans Hübner <hans.huebner at gmail.com> wrote:

> Am So., 7. Feb. 2021 um 09:35 Uhr schrieb Manfred Bergmann <
> manfred.bergmann at me.com>:
>
>> > Am 07.02.2021 um 09:23 schrieb Hans Hübner <hans.huebner at gmail.com>:
>> >
>> > Am So., 7. Feb. 2021 um 09:20 Uhr schrieb Manfred Bergmann <
>> manfred.bergmann at me.com>:
>> > But fundamentally, you also can’t create an instance of a class in
>> Common Lisp from just the symbol. The class definition must be known.
>> >
>> > This simply is untrue.  You can use FIND-CLASS to find a class named by
>> a symbol and then instantiate it.
>>
>> Well, OK. Sure. But when I do that I have again a dependency on the
>> concrete class, or? And it would be similar as knowing the class right from
>> the start.
>>
>
> You don't.  You have a dependency on the name of a class.  The name could
> refer to two entirely different classes between invocations of FIND-CLASS.
> The name could also come from an external source.  Thus, this is purely a
> run-time dependency and it would be quite possible that FIND-CLASS returns
> NIL if given a symbol that does not designate a currently-defined class.
>


-- 
Marco Antoniotti, Associate Professor         tel. +39 - 02 64 48 79 01
DISCo, Università Milano Bicocca U14 2043 http://bimib.disco.unimib.it
Viale Sarca 336
I-20126 Milan (MI) ITALY
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.common-lisp.net/pipermail/pro/attachments/20210207/cd668246/attachment.html>