Pattern, Abstract Factory / Factory

[Manfred Bergmann]

Hi.

> Am 06.02.2021 um 16:14 schrieb Luís Oliveira <luismbo at gmail.com>:
> 
> On Sat, 6 Feb 2021 at 13:46, Manfred Bergmann <manfred.bergmann at me.com> wrote:
>> Does anyone know what Peter Norvig had in mind when he said that metaclasses can be used instead of Abstract Factory pattern?
> 
> Are you talking about slides 12 and 13? Peter does not mention
> metaclasses there or anywhere else in his slides. I believe his point
> is that make-instance is the factory. Classes are first-class values
> and make-instance accepts a class as its first argument. If you use
> qt-backend, gtk-backend, motif-backend classes, at some point you can
> make the decision about which class to instantiate and pass it to
> make-instance. He categorizes this pattern as invisible, which might
> explain why you're having trouble seeing it. :-)

OK. I kind of get it. To simple to be visible. :)

But this is kind of also possible in i.e. Java where you can say:
Foo.class.newInstance() which uses reflection and is not normally used.
But is effectively similar to make-instance `foo.
And yet Abstract Factory pattern in Java exists and is usually done using parallel hierarchies, as he describes.


Manfred