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c# barcode generator library open source PATTERN MATCHING in Font
CHAPTER 5 PATTERN MATCHING Create DataMatrix In None Using Barcode generation for Font Control to generate, create Data Matrix image in Font applications. www.OnBarcode.comPDF-417 2d Barcode Maker In None Using Barcode creator for Font Control to generate, create PDF417 image in Font applications. www.OnBarcode.comIf you re building a web application, you might have particular URLs that need special handling while others get handled in the default manner. The URL can be expressed as a List[String]. We can do the following: Generate GS1 - 12 In None Using Barcode printer for Font Control to generate, create UPC-A Supplement 5 image in Font applications. www.OnBarcode.comGS1 128 Generation In None Using Barcode generator for Font Control to generate, create EAN / UCC - 13 image in Font applications. www.OnBarcode.comdef handleRequest(req: List[String])( exceptions: PartialFunction[List[String], String]): String = if (exceptions.isDefinedAt(req)) exceptions(req) else "Handling URL "+req+" in the normal way" Code 128 Code Set B Creator In None Using Barcode encoder for Font Control to generate, create Code 128 Code Set B image in Font applications. www.OnBarcode.comEAN13 Creator In None Using Barcode generator for Font Control to generate, create UPC - 13 image in Font applications. www.OnBarcode.comSo, if the partial function exceptions (the pattern) matches the request req according to the isDefinedAt method, then we allow the request to be handled by the exceptions function. Otherwise, we do default handling. We can call handleRequest and handle any api requests by a separate handler: Drawing Code 39 Full ASCII In None Using Barcode printer for Font Control to generate, create ANSI/AIM Code 39 image in Font applications. www.OnBarcode.comUSS-93 Creation In None Using Barcode creation for Font Control to generate, create USD-3 image in Font applications. www.OnBarcode.comhandleRequest("foo" :: Nil) { case "api" :: call :: params => doApi(call, params) } def doApi(call: String, params: List[String]): String = "Doing API call "+call Generating Data Matrix ECC200 In Java Using Barcode maker for Java Control to generate, create Data Matrix image in Java applications. www.OnBarcode.comCreating DataMatrix In VS .NET Using Barcode generation for ASP.NET Control to generate, create Data Matrix image in ASP.NET applications. www.OnBarcode.comPartial functions can be composed into a single function using the orElse method.5 So, we can define a couple of partial functions: Scanning Code 128 Code Set C In .NET Framework Using Barcode reader for Visual Studio .NET Control to read, scan read, scan image in Visual Studio .NET applications. www.OnBarcode.comRecognize EAN / UCC - 13 In Visual Studio .NET Using Barcode reader for .NET framework Control to read, scan read, scan image in Visual Studio .NET applications. www.OnBarcode.comval f1: PartialFunction[List[String], String] = { case "stuff" :: Nil => "Got some stuff" } val f2: PartialFunction[List[String], String] = { case "other" :: params => "Other: "+params } Generate EAN / UCC - 13 In Java Using Barcode creation for Java Control to generate, create UPC - 13 image in Java applications. www.OnBarcode.comPrint PDF 417 In Visual Studio .NET Using Barcode printer for Reporting Service Control to generate, create PDF-417 2d barcode image in Reporting Service applications. www.OnBarcode.comAnd we can compose them: PDF417 Generation In None Using Barcode generation for Software Control to generate, create PDF417 image in Software applications. www.OnBarcode.comPrint Barcode In None Using Barcode encoder for Office Word Control to generate, create Barcode image in Word applications. www.OnBarcode.comval f3 = f1 orElse f2
Code 39 Decoder In Java Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications. www.OnBarcode.comCreate Code 128 In Java Using Barcode drawer for Java Control to generate, create Code 128 Code Set B image in Java applications. www.OnBarcode.comAnd we can pass them into the handleRequest method: Generating Barcode In Objective-C Using Barcode encoder for iPhone Control to generate, create Barcode image in iPhone applications. www.OnBarcode.comPainting 2D Barcode In VB.NET Using Barcode maker for Visual Studio .NET Control to generate, create Matrix Barcode image in .NET framework applications. www.OnBarcode.comhandleRequest("a" :: "b" :: Nil)(f3) 5. Technically, combining multiple partial functions using orElse is not functional composition. A roomful of wicked smart functional developers at LShift (http://lshift.com) were unable to come up with a good name other than functional smooshing. CHAPTER 5 PATTERN MATCHING
In this way, Scala gives you a very nice, declarative way of handling complex filtering tasks. Partial functions can match on data and can be passed around like any other instances in Scala. Partial functions replace a lot of the XML configuration files in Java because pattern matching gives you the same declarative facilities as a configuration file, but they are type-safe, high-performance, and they can have guards and generally take advantage of any method in your code. Here s an example of using pattern matching to dispatch REST request in the ESME6 code:7 def dispatch: LiftRules.DispatchPF = { case Req("api" :: "status" :: Nil, "", GetRequest) => status case Req("api" :: "messages" :: Nil, "", GetRequest) => getMsgs case Req("api" :: "messages" :: "long_poll" :: Nil, "", GetRequest) => waitForMsgs case Req("api" :: "messages" :: Nil, "", PostRequest) => () => sendMsg(User.currentUser.map(_.id.is), S) case Req("api" :: "follow" :: Nil, _, GetRequest) => following(calcUser) case Req("api" :: "followers" :: Nil, _, GetRequest) => followers(calcUser) case Req("api" :: "follow" :: Nil, _, PostRequest) => performFollow(S.param("user")) } Object-Oriented and Functional Tensions
At this point, the hard-core object-oriented designer folks may be somewhat unhappy about Scala case class s exposure of lots of internal information. Data hiding is an important part of OOP s abstraction. But in fact, most of the Java classes we define have getters and setters, so there is data exposed in OOP. But there is a tension between the amount of internal state that s exposed in our program and the amount of state that s hidden. In this section, we ll explore OOP and functional programming (FP) patterns for data hiding and exposure. Another tension in OOP is how to define methods on class and interface hierarchies. Where does a method definition belong What happens when a library is deployed but it s necessary to add new functionality to subclasses How do we retrofit the defined-in-stone 6. ESME is the Enterprise Social Messaging Experiment (http://blog.esme.us). 7. This code will not compile without the rest of the ESME code, but it serves as an illustration of using pattern matching as an alternative to XML configuration files or annotations. CHAPTER 5 PATTERN MATCHING
library classes to add this functionality Put more concretely, if we have a library of shapes circle, square, rectangle that each have an area method but hide all their other data, how do we add a perimeter method to the shapes Let s explore the tension and the tools Scala and FP give us to address the tension.
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