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A class diagram exemplifying the singleton pattern.. In object-oriented programming, the singleton pattern is a software design pattern that restricts the instantiation of a class to a singular instance.
Allow concurrent threads to create multiple flyweight instances, thus eliminating contention and allowing multiple instances per value. To enable safe sharing between clients and threads, flyweight objects can be made into immutable value objects , where two instances are considered equal if their values are equal.
Design Patterns: Elements of Reusable Object-Oriented Software (1994) is a software engineering book describing software design patterns.The book was written by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, with a foreword by Grady Booch.
Whereas the singleton allows only one instance of a class to be created, the multiton pattern allows for the controlled creation of multiple instances, which it manages through the use of a map. Rather than having a single instance per application (e.g. the java.lang.Runtime object in the Java programming language ) the multiton pattern instead ...
Function object: with a single method (in C++, the function operator, operator()) it acts much like a function; Immutable object: does not change state after creation; First-class object: can be used without restriction; Container object: contains other objects; Factory object: creates other objects
Making a shallow copy of a const or immutable value removes the outer layer of immutability: Copying an immutable string (immutable(char[])) returns a string (immutable(char)[]). The immutable pointer and length are being copied and the copies are mutable. The referred data has not been copied and keeps its qualifier, in the example immutable.
System.Threading.ThreadPool is configured to have a predefined number of threads to allocate. When the threads are returned, they are available for another computation. Thus, one can use threads without paying the cost of creation and disposal of threads. The following shows the basic code of the object pool design pattern implemented using C#.
See Singleton pattern. A singleton is also a variable that is only used once in a program, usually indicating a programming mistake. See singleton variable. From the start of the term 'Singleton pattern': In software engineering, the singleton design pattern is designed to restrict instantiation of a class to one (or a few) objects.