3. Delegates and events, C#

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//3. Delegates and events

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        //Delegate is a type that can point to a function with certain signature.
        delegate bool TestPointer(int a);  //Instances of a TestPointer can point to any function that takes int and returns bool
        
        //An event is a special method that can be subscribed to and fired
        static event TestPointer SomeEvent; //You can only subscribe functions that take int and return bool to this event. This is declared by using TestPointer delegate
        
        public static void Main(string[] args)
        {
            TestPointer test_function = f => f > 5;
            //Same as:
            //TestPointer test_function = f => 
            //{
            //    return f > 5;
            //};
            
            Console.WriteLine(test_function(6));

SomeEvent += SomeFunction; //+= means subscribe to this event, -= is unsubscribe
            SomeEvent += f => {Console.WriteLine("Hey 2! " + f); return true;}; //another one
            
            SomeEvent(25); //fire! All subscribees will be called in the order they subscribed.
            
        }
        
        public static bool SomeFunction(int a)
        {
            Console.WriteLine("Hey! " + a);
            return true;
        }
    }
}

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Compilation time: 0.08 sec, absolute running time: 0.09 sec, cpu time: 0.08 sec, average memory usage: 17 Mb, average nr of threads: 4