Predicate Delegates in C#

Question

Can you explain to me:

• What is a Predicate Delegate?
• Where should we use predicates?
• Any best practices when using predicates?

Answer 1

Predicate falls under the category of generic delegates in C#. This is called with one argument and always return the boolean type. Basically, the predicate is used to test the condition - true/false. Many classes support predicate as an argument. For example, list.findall expects the parameter predicate. Here is an example of predicate.

Imagine a function pointer with the signature:

 bool delegate myDelegate(T match);

Here is the example:

Node.cs:

namespace PredicateExample
{
    class Node
    {
        public string Ip_Address { get; set; }
        public string Node_Name { get; set; }
        public uint Node_Area { get; set; }
    }
}

Main class:

using System;
using System.Threading;
using System.Collections.Generic;

namespace PredicateExample
{
    class Program
    {
        static void Main(string[] args)
        {
            Predicate backboneArea = Node =>  Node.Node_Area == 0 ;
            List Nodes = new List();
            Nodes.Add(new Node { Ip_Address = "1.1.1.1", Node_Area = 0, Node_Name = "Node1" });
            Nodes.Add(new Node { Ip_Address = "2.2.2.2", Node_Area = 1, Node_Name = "Node2" });
            Nodes.Add(new Node { Ip_Address = "3.3.3.3", Node_Area = 2, Node_Name = "Node3" });
            Nodes.Add(new Node { Ip_Address = "4.4.4.4", Node_Area = 0, Node_Name = "Node4" });
            Nodes.Add(new Node { Ip_Address = "5.5.5.5", Node_Area = 1, Node_Name = "Node5" });
            Nodes.Add(new Node { Ip_Address = "6.6.6.6", Node_Area = 0, Node_Name = "Node6" });
            Nodes.Add(new Node { Ip_Address = "7.7.7.7", Node_Area = 2, Node_Name = "Node7" });

            foreach( var item in Nodes.FindAll(backboneArea))
            {
                Console.WriteLine("Node Name " + item.Node_Name + " Node IP Address " + item.Ip_Address);
            }

            Console.ReadLine();
        }
    }
}