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Typically, the base class template will take advantage of the fact that member function bodies (definitions) are not instantiated until long after their declarations, and will use members of the derived class within its own member functions, via the use of a cast; e.g.:
Object pooling can offer a significant performance boost in situations where the cost of initializing a class instance is high and the rate of instantiation and destruction of a class is high – in this case objects can frequently be reused, and each reuse saves a significant amount of time.
In computer programming, lazy initialization is the tactic of delaying the creation of an object, the calculation of a value, or some other expensive process until the first time it is needed.
Before a class derived from an abstract class can be instantiated, all abstract methods of its parent classes must be implemented by some class in the derivation chain. [ 25 ] Most object-oriented programming languages allow the programmer to specify which classes are considered abstract and will not allow these to be instantiated.
abstract - Specifies that a class only serves as a base class and cannot be instantiated. static - Used only for member classes, specifies that the member class does not belong to a specific instance of the containing class. final - Classes marked as final cannot be extended from and cannot have any subclasses.
Class templates are generally used to implement containers. A class template is instantiated by passing a given set of types to it as template arguments. [5] The C++ Standard Library contains many class templates, in particular the containers adapted from the Standard Template Library, such as vector.
Declaring all constructors of the class to be private, which prevents it from being instantiated by other objects Providing a static method that returns a reference to the instance The instance is usually stored as a private static variable ; the instance is created when the variable is initialized, at some point before when the static method ...
Any call to a class (static or constructor call), triggers the static constructor execution. Static constructors are thread safe and implement a singleton pattern. When used in a generic programming class, static constructors are called at every new generic instantiation one per type. [8]: 38 [4]: 111 Static variables are instantiated as well.