Predicate Delegates

Question

Hi, Can anyone explain where to use predicate delegates . Explain with real example. Also how does it helps in Object oriented design. Thanks Ravi

Vulpes · Answer

A 'predicate delegate' represents a named or anonymous method which has a bool return type i.e. it returns true or false. Such a method can have any number of parameters and can also be generic. Predicate delegates are useful for searching or filtering a collection. If they are also generic then they are particularly useful in object oriented design because they eliminate the need to include such functionality in the collection class itself. A good example of a predicate delegate is the Enumerable.Where extension method which can filter any enunerable collection. For instance: using System; using System.Linq; class Program { static void Main() { int[] ia = {1, 3, 4, 5, 6, 2, 9}; // filter out even numbers var filter = ia.Where(i => i % 2 == 0); foreach(int j in filter) Console.Write("{0} ", j); Console.WriteLine(); string[] sa = {"Adam", "Ben", "John", "Alan", "Ahmed", "Sam", "Ravi"}; // filter out names beginning with 'A' var filter2 = sa.Where(s => s[0] == 'A'); foreach(string t in filter2) Console.Write("{0} ", t); Console.ReadKey(); } } The output is: 4 6 2 Adam Alan Ahmed

Predicate Delegates

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