c# barcode generator library open source PATTERN MATCHING in Font

Generator DataMatrix in Font PATTERN MATCHING

CHAPTER 5 PATTERN MATCHING
Creating DataMatrix In None
Using Barcode maker for Font Control to generate, create DataMatrix image in Font applications.
www.OnBarcode.com
ANSI/AIM Code 39 Printer In None
Using Barcode creation for Font Control to generate, create USS Code 39 image in Font applications.
www.OnBarcode.com
Let s run the code and see that it does what we expect:
Create Barcode In None
Using Barcode encoder for Font Control to generate, create Barcode image in Font applications.
www.OnBarcode.com
Barcode Generation In None
Using Barcode drawer for Font Control to generate, create Barcode image in Font applications.
www.OnBarcode.com
scala> noPairs(List(1,2,3,3,3,4,1,1))
PDF-417 2d Barcode Printer In None
Using Barcode generation for Font Control to generate, create PDF-417 2d barcode image in Font applications.
www.OnBarcode.com
Encoding Code 128 Code Set C In None
Using Barcode drawer for Font Control to generate, create Code 128A image in Font applications.
www.OnBarcode.com
res6: List[Int] = List(1, 2, 3, 4, 1)
Generating GTIN - 13 In None
Using Barcode generator for Font Control to generate, create European Article Number 13 image in Font applications.
www.OnBarcode.com
USD-4 Generator In None
Using Barcode maker for Font Control to generate, create Codabar image in Font applications.
www.OnBarcode.com
Pattern matching can match against constants as well as extract information. Say we have a List[String] and we want to implement a rule that says that we discard the element preceding the ignore String. In this case, we ll use pattern matching to test as well as extract:
DataMatrix Generator In None
Using Barcode encoder for Font Control to generate, create ECC200 image in Font applications.
www.OnBarcode.com
Paint Data Matrix ECC200 In None
Using Barcode encoder for Word Control to generate, create DataMatrix image in Microsoft Word applications.
www.OnBarcode.com
def ignore(in: List[String]): List[String] = in match { case Nil => Nil case _ :: "ignore" :: rest => ignore(rest) // If the second element in the List is "ignore" then return the ignore // method run on the balance of the List case x :: rest => x :: ignore(rest) // return a List created with the first element of the List plus the // value of applying the ignore method to the rest of the List }
QR Code 2d Barcode Printer In Visual Studio .NET
Using Barcode creator for ASP.NET Control to generate, create Quick Response Code image in ASP.NET applications.
www.OnBarcode.com
Create Barcode In None
Using Barcode creation for Online Control to generate, create Barcode image in Online applications.
www.OnBarcode.com
Let s compare this code to Java code that does the same thing. In the Scala code, the pattern matching takes care of length testing and other plumbing. Additionally, because the Scala code is recursive, there s no need for explicit looping or for setting up the accumulator. Looking at the Java code, there s a lot of boilerplate. The logic of incrementing the loop counter exists in different places, and the test (x < len - 1) is not intuitive. In fact, when I wrote the example, I got this test wrong; it wasn t until I ran the code that I discovered the problem.
USS Code 128 Creation In VB.NET
Using Barcode printer for VS .NET Control to generate, create USS Code 128 image in Visual Studio .NET applications.
www.OnBarcode.com
Barcode Printer In Visual Basic .NET
Using Barcode drawer for .NET Control to generate, create Barcode image in Visual Studio .NET applications.
www.OnBarcode.com
public ArrayList<String> ignore(ArrayList<String> in) { ArrayList<String> ret = new ArrayList<String>(); int len = in.size();
Barcode Decoder In Java
Using Barcode Control SDK for BIRT reports Control to generate, create, read, scan barcode image in BIRT reports applications.
www.OnBarcode.com
UPC-A Supplement 5 Maker In Visual Studio .NET
Using Barcode maker for ASP.NET Control to generate, create UPC-A Supplement 2 image in ASP.NET applications.
www.OnBarcode.com
CHAPTER 5 PATTERN MATCHING
Recognizing Barcode In Visual C#.NET
Using Barcode Control SDK for VS .NET Control to generate, create, read, scan barcode image in Visual Studio .NET applications.
www.OnBarcode.com
Generating ECC200 In Visual C#.NET
Using Barcode creator for .NET framework Control to generate, create Data Matrix 2d barcode image in Visual Studio .NET applications.
www.OnBarcode.com
for (int x = 0; x < len;) { if (x < len - 1 && in.get(x + 1).equals("ignore")) { x += 2; } else { ret.add(in.get(x)); x++; } } return ret; }
EAN13 Encoder In Java
Using Barcode creator for Java Control to generate, create GS1 - 13 image in Java applications.
www.OnBarcode.com
Data Matrix ECC200 Printer In Objective-C
Using Barcode generator for iPad Control to generate, create DataMatrix image in iPad applications.
www.OnBarcode.com
We ve seen how to use pattern matching and Lists with extraction and equality testing. We can also use the class test/cast mechanism to find all the Strings in a List[Any]:
def getStrings(in: List[Any]): List[String] = in match { case Nil => Nil case (s: String) :: rest => s :: getStrings(rest) case _ :: rest => getStrings(rest) }
However, the paradigmatic way of filtering a List[Any] into a List of a particular type is by using a pattern as a function. We ll see this in the Pattern Matching As Functions section. In this section, we ve explored how to do pattern matching. We ve seen extraction and pattern matching with Lists. It may seem that List is a special construct in Scala, but there s nothing special about List in Scala. Let s look a little more at case classes.
Nested Pattern Matching in Case Classes
Case classes can contain other case classes, and the pattern matching can be nested. Further, case classes can subclass other case classes. For example, let s create the MarriedPerson subclass of Person:
case class MarriedPerson(override val name: String, override val age: Int, override val valid: Boolean, spouse: Person) extends Person(name, age, valid)
We ve defined the class. Note that the override val syntax is ugly. It s one of the ugliest bits in Scala.
CHAPTER 5 PATTERN MATCHING
And let s create a new instance of MarriedPerson:
scala> val sally = MarriedPerson("Sally", 24, true, p)
sally: MarriedPerson = MarriedPerson(Sally,24,true,Person(David,45,true))
Let s create a method that returns the name of someone who is older or has a spouse who is older:
def mOlder(p: Person): Option[String] = p match { case Person(name, age, true) if age > 35 => Some(name) case MarriedPerson(name, _, _, Person(_, age, true)) if age > 35 => Some(name) case _ => None }
Let s see the new method in action:
scala> mOlder(p)
res7: Option[String] = Some(David)
scala> mOlder(sally)
res8: Option[String] = Some(Sally)
Scala s case classes give you a lot of flexibility for pattern matching, extracting values, nesting patterns, and so on. You can express a lot of logic in pattern declarations. Further, patterns are easy for people to read and understand, which makes code maintenance easier. And because Scala is statically typed, the compiler will help detect some code problems.
Copyright © OnBarcode.com . All rights reserved.