C# compiler complains that abstract class does not implement interface?
You must add an abstract stub of the method: public abstract ITask CreateTask(TaskId id); Inheritors can then override it to implement the interface.
inheritance
How to find source_location of the code executed by super?
From ruby 2.2 you can use super_method like this: Class A def pr puts “pr” end end Class B < A def pr puts “Super method: #{method(:pr).super_method}” end end As super_method returns a Method, you can chain them to find the ancestor: def ancestor(m) m = method(m) if m.is_a? Symbol super_m = m.super_method if super_m.nil? … Read more
Force base method call
There isn’t and shouldn’t be anything to do that. The closest thing I can think of off hand if something like having this in the base class: public virtual void BeforeFoo(){} public void Foo() { this.BeforeFoo(); //do some stuff this.AfterFoo(); } public virtual void AfterFoo(){} And allow the inheriting class override BeforeFoo and/or AfterFoo
Python – inheriting from old-style classes
You need to call the constructor like this: telnetlib.Telnet.__init__(self, host, port, timeout) You need to add the explicit self since telnet.Telnet.__init__ is not a bound method but rather an unbound method, i.e. witout an instance assigned. So when calling it you need to pass the instance explicitely. >>> Test.__init__ <unbound method Test.__init__> >>> Test().__init__ <bound … Read more
JPA Inheritance demands ID in subclass
I solved it myself by creating a MappedSuperclass @MappedSuperclass public abstract class EntityBase{ @Id @GeneratedValue private int id; …setter/getter } All entities are inheriting from this class. I am still wondering why the tutorials dont mention this, but maybe it gets better with the JPA 2 implementations.
How to create foreign key that is also a primary key in MySQL?
Add FOREIGN KEY (sale_id) REFERENCES Sale(sale_id) to each foreign table: CREATE TABLE Sale( sale_id CHAR(40), PRIMARY KEY(sale_id), discount DOUBLE, type VARCHAR(255), price DOUBLE ) ENGINE=INNODB; CREATE TABLE Normal_Sale( sale_id CHAR(40), PRIMARY KEY(sale_id), FOREIGN KEY (sale_id) REFERENCES Sale(sale_id) ) ENGINE=INNODB; CREATE TABLE Special_Sale( sale_id CHAR(40), PRIMARY KEY(sale_id), FOREIGN KEY (sale_id) REFERENCES Sale(sale_id) ) ENGINE=INNODB; Just make … Read more
Enum inheriting from int
According to the documentation: Every enumeration type has an underlying type, which can be any integral type except char. The default underlying type of the enumeration elements is int. So, no, you don’t need to use int. It would work with any integral type. If you don’t specify any it would use int as default … Read more
Inheritance or composition: Rely on “is-a” and “has-a”?
No – “is a” does not always lead to inheritence. A well cited example is the relationship between a square and a rectangle. A square is a rectangle, but it will be bad to design code that inherits a Square class off a Rectangle class. My suggestion is to enhance your “is a / has … Read more
Is there way for a class to ‘remove’ methods that it has inherited?
No – this would violate Liskov’s Substitution Principle. You should always be able to use an instance of a subtype as if it were an instance of a supertype. Don’t forget that a caller may only be aware of your type “as” the base type or an interface. Consider this code: object foo = new … Read more
How to override static method of template class in derived class
What you’re trying to do is not achievable with simple class inheritance; a method cannot be both static and virtual. You need a static method to be able to call a function without an object (an instance); and you need bar to be virtual so that bar<int>::foo() calls derived::bar() when called from a derived instance. … Read more