Module Gnumed.pycommon.gmBorg

# -*- coding: utf-8 -*-
"""A base class turning child classes into a Singleton."""

__author__ = "Karsten.Hilbert@gmx.net"
__license__ = "GPL v2 or later"

#===================================================
class cBorg:
        """A generic Borg mixin for new-style classes.

        - mixin this class with your class' ancestors to borg it

        - there may be many _instances_ of this - PER CHILD CLASS - but they all share _state_
        """
        _instances:dict = {}

        def __new__(cls, *args, **kargs):
                # look up subclass instance cache
                if cBorg._instances.get(cls) is None:
                        #cBorg._instances[cls] = object.__new__(cls, *args, **kargs)
                        cBorg._instances[cls] = object.__new__(cls)
                return cBorg._instances[cls]

#===================================================
if __name__ == '__main__':

        import sys

        if len(sys.argv) < 2:
                sys.exit()

        if sys.argv[1] != 'test':
                sys.exit()

        class A(cBorg):
                pass

        class B(cBorg):
                pass

        class C(cBorg):
                def __init__(self, val='default'):
                        self.x = val

        #===================================================
        print("testing new-style classes borg")
        a1 = A()
        a2 = A()
        a1.a = 5                                                                        # type: ignore
        print(a1.a, "==", a2.a)                                         # type: ignore
        a3 = A()
        print(a1.a, "==", a2.a, "==", a3.a)                     # type: ignore
        b1 = B()
        b1.a = 10                                                                       # type: ignore
        print(b1.a)                                                                     # type: ignore
        print(a1.a)                                                                     # type: ignore
        b2 = B()
        print(b2.a)                                                                     # type: ignore

        c1 = C(val = 'non-default')
        print(c1.x)
        c2 = C(val = 'non-default 2')
        print(c2.x)
        c3 = C()
        print(c3.x)

#===================================================