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The observer design pattern is a behavioural pattern listed among the 23 well-known "Gang of Four" design patterns that address recurring design challenges in order to design flexible and reusable object-oriented software, yielding objects that are easier to implement, change, test and reuse. [1]
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 .
ReactiveX is a combination of ideas from the observer and the iterator patterns and from functional programming. [2] An observer subscribes to an observable sequence. The sequence then sends the items to the observer one at a time, usually by calling the provided callback function. The observer handles each one before processing the next one.
Signals and slots is a language construct introduced in Qt [1] for communication between objects which makes it easy to implement the observer pattern while avoiding boilerplate code. The concept is that GUI widgets , and other objects, can send signals containing event information which can be received by other objects using special member ...
[2] considers the Observer pattern and Publish/Subscribe to be the same thing. Some may consider the Observer object to be one participant (the "broker") in Publish/Subscribe, but that doesn't seem like a good reason to have a separate article. -- Beland 23:41, 14 May 2009 (UTC) Observer pattern is not the same thing as Publish/Subscribe.
The curiously recurring template pattern (CRTP) is an idiom, originally in C++, in which a class X derives from a class template instantiation using X itself as a template argument. [1] More generally it is known as F-bound polymorphism , and it is a form of F -bounded quantification .
David E. DeLano of C++ Report praised the first volume, writing, "Overall this text is good and I recommend it as an addition to any collection of books on patterns." He said "some of the language and grammar usage feels awkward to the reader" and some of the book has "stiffness and flow problems". [1]
The indirection pattern supports low coupling and reuses potential between two elements by assigning the responsibility of mediation between them to an intermediate object. An example of this is the introduction of a controller component for mediation between data (model) and its representation (view) in the model-view-controller pattern.