**Introduction under construction**
Here I implement and compare the 3 patterns:
Unique
#Unique Pattern
class Unique:
#Define some static variables here
x = 1
@classmethod
def init(cls):
#Define any computation performed when assigning to a "new" object
return cls
Singleton
#Singleton Pattern
class Singleton:
__single = None
def __init__(self):
if not Singleton.__single:
#Your definitions here
self.x = 1
else:
raise RuntimeError('A Singleton already exists')
@classmethod
def getInstance(cls):
if not cls.__single:
cls.__single = Singleton()
return cls.__single
Borg
#Borg Pattern
class Borg:
__monostate = None
def __init__(self):
if not Borg.__monostate:
Borg.__monostate = self.__dict__
#Your definitions here
self.x = 1
else:
self.__dict__ = Borg.__monostate
Test
#SINGLETON
print "\nSINGLETON\n"
A = Singleton.getInstance()
B = Singleton.getInstance()
print "At first B.x = {} and A.x = {}".format(B.x,A.x)
A.x = 2
print "After A.x = 2"
print "Now both B.x = {} and A.x = {}\n".format(B.x,A.x)
print "Are A and B the same object? Answer: {}".format(id(A)==id(B))
#BORG
print "\nBORG\n"
A = Borg()
B = Borg()
print "At first B.x = {} and A.x = {}".format(B.x,A.x)
A.x = 2
print "After A.x = 2"
print "Now both B.x = {} and A.x = {}\n".format(B.x,A.x)
print "Are A and B the same object? Answer: {}".format(id(A)==id(B))
#UNIQUE
print "\nUNIQUE\n"
A = Unique.init()
B = Unique.init()
print "At first B.x = {} and A.x = {}".format(B.x,A.x)
A.x = 2
print "After A.x = 2"
print "Now both B.x = {} and A.x = {}\n".format(B.x,A.x)
print "Are A and B the same object? Answer: {}".format(id(A)==id(B))
Output:
SINGLETONAt first B.x = 1 and A.x = 1 After A.x = 2 Now both B.x = 2 and A.x = 2 Are A and B the same object? Answer: True BORG At first B.x = 1 and A.x = 1 After A.x = 2 Now both B.x = 2 and A.x = 2 Are A and B the same object? Answer: False UNIQUE At first B.x = 1 and A.x = 1 After A.x = 2 Now both B.x = 2 and A.x = 2 Are A and B the same object? Answer: True
In my opinion, Unique implementation is the easiest, then Borg and finally Singleton with an ugly number of two functions needed for its definition.
No hay comentarios:
Publicar un comentario