Pattern, Abstract Factory / Factory

[Luís Oliveira]

On Sat, 6 Feb 2021 at 16:29, Manfred Bergmann <manfred.bergmann at me.com> wrote:
> 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.

 My Java is getting rustier and rustier, but maybe you can tell me why
the following program doesn't compile:

class Foo { }
class Bar extends Foo { }
class Baz extends Foo { }

class Main {
  public static void main(String[] args) {
    makeAndPrint(Foo.class);
    makeAndPrint(Bar.class);
    makeAndPrint(Baz.class);
  }

  public static void makeAndPrint(Class<Foo> klass) {
    try {
      Object o = klass.newInstance(klass);
      System.out.println("Created: " + o.toString());
    } catch (Exception e) {
      System.err.println("Failed: " + klass);
    }
  }
}

The rough equivalent in Common Lisp would be:

(defclass foo () ())
(defclass bar (foo) ())
(defclass baz (foo) ())

(mapcar #'make-instance '(foo bar baz))

Luís