I’m answering my own question, since I eventually decided that I really do want to subclass Dict, rather than creating a new mapping class, and UserDict still defers to the underlying Dict object in some cases, rather than using the provided __setitem__. After reading and re-reading the Python 2.6.4 source (mostly Objects/dictobject.c, but I grepped … Read more
There are no abstract classes in Swift (just like Objective-C). Your best bet is going to be to use a Protocol, which is like a Java Interface. With Swift 2.0, you can then add method implementations and calculated property implementations using protocol extensions. Your only restrictions are that you can’t provide member variables or constants … Read more
When you specify cls: A, you’re saying that cls expects an instance of type A. The type hint to specify cls as a class object for the type A (or its subtypes) uses typing.Type. from typing import Type def process_any_subclass_type_of_A(cls: Type[A]): pass From The type of class objects : Sometimes you want to talk about … Read more
What you should do: Add a constructor to your super class: public Superclass { public SuperClass(String flavour) { // super class constructor this.flavour = flavour; } } In the Crisps class: public Crisps(String flavour, int quantity) { super(flavour); // send flavour to the super class constructor this.quantity = quantity; } Comments Some comments to … Read more
This won’t compile since Animal does not have a method called bark. Think of it this way, all dogs are animals, but not all animals are dogs. All dogs bark, but not all animals bark.
Your nested class (which isn’t a subclass, by the way) isn’t marked as being static, therefore it’s an inner class which requires an instance of the encoding class (JavaApp1) in order to construct it. Options: Make the nested class static Make it not an inner class (i.e. not within JavaApp1 at all) Create an instance … Read more
The crucial distinction between Python’s __init__ and those other languages constructors is that __init__ is not a constructor: it’s an initializer (the actual constructor (if any, but, see later;-) is __new__ and works completely differently again). While constructing all superclasses (and, no doubt, doing so “before” you continue constructing downwards) is obviously part of saying … Read more
It doesn’t create two objects, only one: B. When inheriting from another class, you must call super() in your constructor. If you don’t, the compiler will insert that call for you as you can plainly see. The superclass constructors are called because otherwise the object would be left in an uninitialized state, possibly unbeknownst to … Read more
The Cocoa frameworks take the approach that the Object Composition pattern is more appropriate than traditional class hierarchy. In general, this means that there is likely to be a property on UIButton where you can set another object to handle various aspects of the button. This is the preferred way to “customize” how your button … Read more
int is immutable so you can’t modify it after it is created, use __new__ instead class TestClass(int): def __new__(cls, *args, **kwargs): return super(TestClass, cls).__new__(cls, 5) print TestClass()