What is predicate delegate in C#

A predicate is a function that returns Boolean true or false. A predicate delegate is a reference to a predicate.A predicate delegate is a delegate with the following signature:

•          Return type - bool
•          Argument type - generic

A predicate delegate thus is a delegate which is capable of taking any custom type as an argument. Predicates are very useful for filtering a list of values - here is an example.

using System;

using System.Collections.Generic;

public class Program

    {

        private static void Main(string[] args)

        {

            var list = new List<string> { "abc",  "xyz", "pqr"};

            var predicate = new Predicate<string>(EqualToAbc);

            var newList = list.FindAll(predicate);

        } 

        private static bool EqualToAbc(string arg)

        {

            return arg.Equals("abc");

        }

    }

Now if you are using C # 3 Or Later versions you can use a lambda to represent the predicate in a cleaner fashion:

using System;

using System.Collections.Generic;

public class Program

    {

        private static void Main(string[] args)

        {

            var list = new List<string> { "abc",  "xyz", "pqr"};          

            var newList = list.FindAll(i => i.Equals(("abc");

        }    

    }