The drawbacks are that All classes will have to initialize all its virtual bases all the time (e.g. if A is virtual base of B, and C derives from B, it also have to initialize A itself). You have to use more expensive dynamic_cast everywhere you use a static_cast (may or may not be the … Read more
The C++11 Standard says (ยง10.1) [class.mi]: The order of derivation is not significant except as specified by the semantics of initialization by constructor (12.6.2), cleanup (12.4), and storage layout (9.2, 11.1). The three referenced paragraphs reveal that Constructors are called in the order you write them down (first base class in the list is constructed … Read more
The problem in your case is that the classes you try to inherit from have different metaclasses: >>> type(QStandardItem) <class ‘sip.wrappertype’> >>> type(ConfigParser) <class ‘abc.ABCMeta’> Therefore python can’t decide which should be the metaclass for the newly created class. In this case, it would have to be a class inheriting from both sip.wrappertype (or PyQt5.QtCore.pyqtWrapperType … Read more
Multiple inheritance of implementations is not allowed. Components can inherit multiple interfaces, though. Inheriting multiple interfaces isn’t problematic, since you’re simply defining new method signatures to be implemented. It’s the inheritance of multiple copies of functionality that is traditionally viewed as causing problems, or at the very least, confusion (e.g., the diamond of death).
SQLAlchemy version 0.7.3 introduced the __abstract__ directive which is used for abstract classes that should not be mapped to a database table, even though they are subclasses of sqlalchemy.ext.declarative.api.Base. So now you create a base class like this: Base = declarative_base() class CommonRoutines(Base): __abstract__ = True id = Column(Integer, primary_key=True) def __init__(self): # … Notice … Read more
Declaring a constructor on the same interface as the instance members doesn’t really make much sense — if you’re going to pass in a type dynamically to use in a constructor, it’s the static side of the class that would be restricted. What you would want to do is probably something like this: interface Colorable … Read more
For question 2, you need to call super in each class: class First(object): def __init__(self): super(First, self).__init__() print “first” class Second(object): def __init__(self): super(Second, self).__init__() print “second” class Third(First, Second): def __init__(self): super(Third, self).__init__() print “that’s it” For question 3, that can’t be done, your method needs to have the same signature. But you could … Read more
Yes, you’re missing an important detail of generics implementation on JVM: the type erasure. In a nutshell, the compiled bytecode of classes doesn’t actually contain any information about generic types (except for some metadata about the fact that a class or a method is generic). All the type checking happens at compile time, and after … Read more
Indeed you are doing it wrong. If you have simple inheritance, just inherit from enable_shared_from this in the base class, and derived class get it for free. (of course you’ll need to downcast the result) If you have multiple inheritance (like it seems), you must use the trick described here and also here : /* … Read more
Shouldn’t the inheritance be the other way round? In the MRO foo currently comes before bar_for_foo_mixin, and then rightfully complains. With class myfoo(bar_for_foo_mixin, foo) it should work. And I am not sure if your class design is the right way to do it. Since you use a mixin for implementing bar it might be better … Read more