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
The Gang Of Four “Design Patterns; Elements of Reusable Object-Oriented Software” book contains two entries, “Abstract Factory” (aka ‘Virtual Constructor’) and “Factory Method”. I don’t know about “Concrete Factory.” I’ve heard the term, but never given it too much thought. Factory Method In “Factory Method” an object has a method which is responsible for the … Read more
I have stumbled across the same question while investigating these patterns. I think the major differences can be found between a Service Locator and a Factory (whether it is abstract or not): Service Locator ‘Locates’ an existing dependency (the service). Although the service may be created during resolution, it is of no consequence to the … Read more
I agree with your view that a Builder is really just a glorified constructor, and that the “builder pattern is just a way to build an object similar to what a constructor does”. However, here are a few of scenarios where the complexity of constructing an object makes the use of a Builder compelling. Object’s … Read more
Some canonized design patterns — Adapter, Factory, Command, Visitor, etc — are approximations of features which are baked into other languages. Off the top of my head: Event-handlers in C# are baked-in versions of the observer pattern. Think about how you’d wire up events in C# if you had to roll your own observer each … Read more
For my DAO I keep a copy of the original values as retrieved from the database. When I send it to be updated, I simply compare the original values with the current. It costs a little in processing but it is a lot better than having a dirty flag per property. EDIT to further justify … Read more
I’m currently playing around with the Boost.Enum proposal from the Boost Vault (filename enum_rev4.6.zip). Although it was never officially submitted for inclusion into Boost, it’s useable as-is. (Documentation is lacking but is made up for by clear source code and good tests.) Boost.Enum lets you declare an enum like this: BOOST_ENUM_VALUES(Level, const char*, (Abort)(“unrecoverable problem”) … Read more
Publisher-subscriber vs Observer [closed]
As you might have read, the pattern consists of 4 components: ThreadPool, HandleSet, Handle, ConcreteEventHandler (implements the EventHandler interface). You can think of it as a taxi station at night, where all the drivers are sleeping except for one, the leader. The ThreadPool is a station managing many threads – cabs. The leader is waiting … Read more
I think there’s a basic “life cycle of a design pattern” Author writes about design pattern in a book. Book becomes well read, possibly best seller Design pattern enters public conscious, gains mindshare. Design pattern gets used. It works well. design pattern gets more mindshare Design pattern becomes panacea, gets over-used. Different Author writes “Design … Read more