http://scala.sygneca.com// 2010-09-03T01:13:17+01:00 http://scala.sygneca.com// http://scala.sygneca.com//lib/images/favicon.ico text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/component-mixins?rev=1265879458 This pattern is described in the paper Scalable Component Abstractions by Martin Odersky and Matthias Zenger. The term “Cake pattern” was coined later, in this thread: http://www.nabble.com/Inheriting-static-members-td10106162.html . Jo... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/duck-typing-done-right?rev=1265879458 Duck typing is often used in dynamic languages - http://en.wikipedia.org/wiki/Duck_typing. You can do this with scala in a perfectly type safe way using structural types. You can either define the signature in the method signature (as shown in the... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/dynamic-scope?rev=1265879458 'Dynamic scope' pattern Like most modern languages, Scala is lexically scoped, i.e. the scope of a variable is determined by the nesting of braces in the source code. Dynamic scoping instead makes variables available based on the nesting of func... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/gofabstractfactory?rev=1265879458 trait Factory { def create(instanceType:String):Command     }      class FactoryImpl extends Factory{ def create(instanceType:String):Command = instanceType match { case "validate" ... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/gofchainofresponsibility?rev=1265879458 The idea of the pattern is to decouple the sender of a request from the receiver of that request. Essentially the sender is unaware of the chain of handlers; each handler may pass on the request to the next handler in the chain. Here is a straight... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/gofcommand?rev=1265879458 trait Command { def execute():Unit }class ValidateCommand extends Command { def execute{ println("validate command executed ...") } }... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/gofcomposite?rev=1265879458 package pattern   class Activity(val name : String) { protected var nested : List[Activity] = Nil var parent : Option[Activity] = None def subActivities = nested.reverse def level : Int = { var i = 0 fo... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/gofflyweight?rev=1265879458 The Flyweight pattern is a special kind of Memoization where the memoized function is a constructor. This pattern is especially relevant in Scala for implicit conversions to RichFoo objects. ... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/gofsingleton?rev=1265879458 This pattern is elevated to a language construct in Scala. You can use the object keyword to create an object which serves the cause. import scala.collection.jcl._   object MySingleton extends ArrayList{   //create a singleton calle... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/loan?rev=1265879458 Ensures that a resource is deterministically disposed of once it goes out of scope. The normal way to do this in Java is with a try ... finally block, which leads to ugly and fragile code, especially when there are multiple resources: var r : Resou... text/html 2010-04-20T17:25:09+01:00 http://scala.sygneca.com//patterns/memoization?rev=1271780709 In memoization, the results of a function are memoized— recorded in a Map indexed by the function’s argument(s). This saves the computation required to execute the original function as well as reducing memory which which might be used up... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/pattern-replacements?rev=1265879458 Some common patterns may be better implemented using features specific to Scala (or at least less common in other OO languages). Singleton pattern The singleton pattern describes a way to ensure that only one instance of an object exists. Scala&... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/pimp-my-library?rev=1265879458 The name of this pattern comes from Martin Odersky’s article. To illustrate, here’s an example from the mailing list. The goal is to add a headOr method to the standard library List class, without modifying the Scala distribution: We d... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/sidebar?rev=1265879458 Patterns Patterns list Pattern replacements Structural patterns Cake Dynamic scope Utility belt Reactive abstractions Pimp my library Duck typing done right Memoization Behavioural patterns Loan GoF Design Patterns Creational Patte... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/start?rev=1265879458 Scala design patterns This section lists some design patterns which are useful in Scala programs. There’s also the pattern replacements page, which describes ways in which Scala language features make some common patterns unnecessary. ... text/html 2010-02-11T09:10:58+01:00 http://scala.sygneca.com//patterns/utility-belt?rev=1265879458 Let’s consider the problem of organizing the human-readable messages in an application. We have a number of desirable features: Extensibility of existing message bundles Flexibility and choice of messages Separation of message code from lo...