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override - Specifies that a method or property declaration is an override of a virtual member or an implementation of a member of an abstract class. readonly - Declares a field that can only be assigned values as part of the declaration or in a constructor in the same class. unsafe - Specifies an unsafe context, which allows the use of pointers.
In C#, class methods, indexers, properties and events can all be overridden. Non-virtual or static methods cannot be overridden. The overridden base method must be virtual, abstract, or override. In addition to the modifiers that are used for method overriding, C# allows the hiding of an inherited property or method.
Multiple inheritance is a feature of some object-oriented computer programming languages in which an object or class can inherit features from more than one parent object or parent class. It is distinct from single inheritance, where an object or class may only inherit from one particular object or class.
For instance, in C#, the base method or property can only be overridden in a subclass if it is marked with the virtual, abstract, or override modifier, while in programming languages such as Java, different methods can be called to override other methods. [15] An alternative to overriding is hiding the inherited code.
These are detailed in a terminology resembling that of design by contract methodology, leading to some restrictions on how contracts can interact with inheritance: Preconditions cannot be strengthened in the subtype. Postconditions cannot be weakened in the subtype. Invariants cannot be weakened in the subtype. History constraint (the "history ...
Some other limitations on value types are that they cannot derive from each other (but can implement interfaces) and cannot have an explicit default (parameterless) constructor because they already have an implicit one which initializes all contained data to the type-dependent default value (0, null, or alike).
Therefore, both Java and C# treat array types covariantly. For instance, in Java String [] is a subtype of Object [], and in C# string [] is a subtype of object []. As discussed above, covariant arrays lead to problems with writes into the array. Java [4]: 126 and C# deal with this by marking each array object with a type when it is created ...
Finally, introduce a class named Object with members to control its visibility (using a VisibilityDelegate), movability (using an UpdateDelegate), and solidity (using a CollisionDelegate). This class has methods which delegate to its members, e.g. update() simply calls a method on the UpdateDelegate: