abstract-class
What is the point of using abstract methods?
Say you have three printers that you need to write drivers for, Lexmark, Canon, and HP. All three printers will have the print() and getSystemResource() methods. However, print() will be different for each printer, and getSystemResource() remains the same for all three printers. You also have another concern, you would like to apply polymorphism. Since …
Can you cache a virtual function lookup in C++?
There are two costs to a virtual function call: The vtable lookup and the function call. The vtable lookup is already taken care of by the hardware. Modern CPUs (assuming you’re not working on a very simple embedded CPU) will predict the address of the virtual function in their branch predictor and speculatively execute it …
pure-specifier on function-definition
Ok, I’ve just learned something. A pure virtual function must be declared as follows: class Abstract { public: virtual void pure_virtual() = 0; }; It may have a body, although it is illegal to include it at the point of declaration. This means that to have a body the pure virtual function must be defined …
Template or abstract base class?
This depends on your goals. You can use version 1 if you Intend to replace brakes of a car (at runtime) Intend to pass Car around to non-template functions I would generally prefer version 1 using the runtime polymorphism, because it is still flexible and allows you to have the Car still have the same …
Abstract UserControl inheritance in Visual Studio designer
What we want First, let’s define the final class and the base abstract class. public class MyControl : AbstractControl … public abstract class AbstractControl : UserControl // Also works for Form … Now all we need is a Description provider. public class AbstractControlDescriptionProvider<TAbstract, TBase> : TypeDescriptionProvider { public AbstractControlDescriptionProvider() : base(TypeDescriptor.GetProvider(typeof(TAbstract))) { } public override …
invalid new-expression of abstract class type
invalid new-expression of abstract class type ‘box’ There is nothing unclear about the error message. Your class box has at least one member that is not implemented, which means it is abstract. You cannot instantiate an abstract class. If this is a bug, fix your box class by implementing the missing member(s). If it’s by …
Most Pythonic way to declare an abstract class property
You can use the __init_subclass__ method which was introduced in Python 3.6 to make customizing class creation easier without resorting to metaclasses. When defining a new class, it is called as the last step before the class object is created. In my opinion, the most pythonic way to use this would be to make a …
How can I assure a class to have a static property by using interface or abstract?
You can’t do that. Interfaces, abstract, etc. cannot apply to static members. If you want to accomplish this, you will have to manually remember to do it on all deriving classes. Also, static members are inherited by deriving classes. Child classes must hide the static parent member if they wish to specify alternate behavior.
Determine if a Python class is an Abstract Base Class or Concrete
import inspect print(inspect.isabstract(object)) # False print(inspect.isabstract(MessageDisplay)) # True print(inspect.isabstract(FriendlyMessageDisplay)) # True print(inspect.isabstract(FriendlyMessagePrinter)) # False This checks that the internal flag TPFLAGS_IS_ABSTRACT is set in the class object, so it can’t be fooled as easily as your implementation: class Fake: __abstractmethods__ = ‘bluh’ print(is_abstract(Fake), inspect.isabstract(Fake)) # True, False