定义多个has-a关系的最好方法，其中A有-a X，B有-a X，C有-a X

class BaseClass:
    def __init__(self):
        self.x = X()

class A(BaseClass):
    pass

class B(BaseClass):
    pass

class C(BaseClass):
    pass

class X:
    pass

class A:
    def __init__(self):
        self.x = X()

class B:
    def __init__(self):
        self.x = X()

class C:
    def __init__(self):
        self.x = X()

class X:
    pass

class A:
    def __init__(self, x: X):
        self.x = x

class B:
    def __init__(self, x: X):
        self.x = x

class C:
    def __init__(self, x: X):
        self.x = x

# 使用依赖注入创建实例
x_instance = X()
a_instance = A(x_instance)
b_instance = B(x_instance)
c_instance = C(x_instance)

class X:
    pass

class XFactory:
    @staticmethod
    def create_x():
        return X()

class A:
    def __init__(self):
        self.x = XFactory.create_x()

class B:
    def __init__(self):
        self.x = XFactory.create_x()

class C:
    def __init__(self):
        self.x = XFactory.create_x()