In general, a wrapper class is any class which “wraps” or “encapsulates” the functionality of another class or component. These are useful by providing a level of abstraction from the implementation of the underlying class or component; for example, wrapper classes that wrap COM components can manage the process of invoking the COM component without … Read more
I like thinking about design pattens in terms of my classes being ‘people,’ and the patterns are the ways that the people talk to each other. So, to me the factory pattern is like a hiring agency. You’ve got someone that will need a variable number of workers. This person may know some info they … Read more
Proxy, Decorator, Adapter, and Bridge are all variations on “wrapping” a class. But their uses are different. Proxy could be used when you want to lazy-instantiate an object, or hide the fact that you’re calling a remote service, or control access to the object. Decorator is also called “Smart Proxy.” This is used when you … Read more
Yes, singletons are bad. They are bad because all they do for you is combine two properties, each of which is bad about 95% of the time. (Which would mean that on average, singletons are bad 99.75% of the time ;)) A singleton, as defined by the GoF, is a data structure which: Grants global … Read more
Paraphrased from Brian Button: They are generally used as a global instance, why is that so bad? Because you hide the dependencies of your application in your code, instead of exposing them through the interfaces. Making something global to avoid passing it around is a code smell. They violate the single responsibility principle: by virtue … Read more
I would avoid the Singleton approach suggested by Flavius. There are numerous reasons to avoid this approach. It violates good OOP principles. The google testing blog has some good articles on the Singleton and how to avoid it: http://googletesting.blogspot.com/2008/08/by-miko-hevery-so-you-join-new-project.html http://googletesting.blogspot.com/2008/05/tott-using-dependancy-injection-to.html http://googletesting.blogspot.com/2008/08/where-have-all-singletons-gone.html Alternatives a service provider http://java.sun.com/blueprints/corej2eepatterns/Patterns/ServiceLocator.html dependency injection http://en.wikipedia.org/wiki/Dependency_injection and a php explanation: http://components.symfony-project.org/dependency-injection/trunk/book/01-Dependency-Injection This … Read more
I’m not very familiar with the Visitor pattern. Let’s see if I got it right. Suppose you have a hierarchy of animals class Animal { }; class Dog: public Animal { }; class Cat: public Animal { }; (Suppose it is a complex hierarchy with a well-established interface.) Now we want to add a new … Read more
If you define patterns as anti-patterns just because there are some situations where it does not fit, then YES it’s an anti pattern. But with that reasoning all patterns would also be anti patterns. Instead we have to look if there are valid usages of the patterns, and for Service Locator there are several use … Read more
Switch-statements are not an antipattern per se, but if you’re coding object oriented you should consider if the use of a switch is better solved with polymorphism instead of using a switch statement. With polymorphism, this: foreach (var animal in zoo) { switch (typeof(animal)) { case “dog”: echo animal.bark(); break; case “cat”: echo animal.meow(); break; … Read more
To help with answering, here is more about the anti-pattern comment: it is overused, introduces unnecessary restrictions in situations where a sole instance of a class is not actually required, and introduces global state into an application From: http://en.wikipedia.org/wiki/Singleton_pattern For more on this you can look at: https://www.michaelsafyan.com/tech/design/patterns/singleton Here is a great ending to the … Read more