Pattern: Decorator

Description

Decorator allows behavior to be added to an individual object, either statically or dynamically, without affecting the behavior of other objects from the same class.

Example in .NET :

Decorator 

   

namespace Decorator;
internal class DecoratorDemo
{
    public static void Stream_Crypto_Gzip()
    {
        string nameFile = "test.txt";
        if (File.Exists(nameFile))
            File.Delete(nameFile);
        byte[] data = ASCIIEncoding.ASCII.GetBytes("Hello World!");
        //first time we have a stream
        using (var stream = new FileStream(nameFile, FileMode.OpenOrCreate, FileAccess.Write))
        {
            //stream.Write(data, 0, data.Length);
            //return;
            
            var cryptic = new DESCryptoServiceProvider();

            cryptic.Key = ASCIIEncoding.ASCII.GetBytes("ABCDEFGH");
            cryptic.IV = ASCIIEncoding.ASCII.GetBytes("ABCDEFGH");
            //we decorate the initial stream with a crypto stream
            using (var crStream = new CryptoStream(stream, cryptic.CreateEncryptor(), CryptoStreamMode.Write))
            {
                //and we decorate further by encoding
                using (var gz = new GZipStream(crStream, CompressionLevel.Optimal))
                {
                    gz.Write(data, 0, data.Length);
                }

            }
        }
    }
}

Learn More

Wikipedia

Homework

1. Add a logging to DBConnection . 2. Use by decorating a coffee with milk, sugar, and chocolate (and maybe other condiments). The coffee should be able to display the condiments in a Display method and calculate the price of the coffee with milk, sugar, and chocolate.

Pattern: Facade

Description

Facade is is an object that provides a simplified interface to a larger body of code, such as a class library.

Example in .NET :

Facade 

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Infrastructure;

namespace Facade;
internal class FacadeDemo
{
    public static void ExecuteSql()
    {
        MyDbContext cnt = new();
        //calling the facade
        DatabaseFacade dbFacade = cnt.Database;
        dbFacade.EnsureCreated(); 
    }
}

public class MyDbContext:DbContext
{
    
}

Learn More

Wikipedia

Homework

Implement a Facade that will allow you to display a question in a MessageBox with a single method call in a console application and return yes/no as a result.

Pattern: Factory

Description

A factory is a function or method that returns objects of a varying prototype or class from some method call, which is assumed to be new

Example in .NET :

Factory 

 
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Controllers;
using Microsoft.AspNetCore.Mvc.Internal;
using System.Data.Common;
using System.Globalization;
using System.Net;
using System.Web.Mvc;

namespace Factory;
internal class FactoryDemo
{
    public static void DemoWebRequest()
    {
        HttpWebRequest hwr = (HttpWebRequest)WebRequest.Create("http://www.yahoo.com");

    }
    public static void DemoConvert()
    {
        string value = "1,500";
        Thread.CurrentThread.CurrentCulture = CultureInfo.CreateSpecificCulture("en-US");

        Console.WriteLine(Convert.ToDouble(value));

        Thread.CurrentThread.CurrentCulture = CultureInfo.CreateSpecificCulture("fr-FR");
        Console.WriteLine(Convert.ToDouble(value));

    }
    static void RegisterControllerFactory()
    {
        ControllerBuilder.Current.SetControllerFactory(new MyControllerFactory());
    }
}

//default controller factory is a factory of controllers
class MyControllerFactory : System.Web.Mvc.DefaultControllerFactory
{

    public override IController CreateController(System.Web.Routing.RequestContext requestContext, string controllerName)
    {
        if (controllerName == "andrei")
            return null;//maybe controller not found

        return base.CreateController(requestContext, controllerName);
    }
}

Learn More

Wikipedia

Homework

having multiple types of drinks( water, tea, coffee) with an IDrink interface create a factory method ( with a parameter ) to create a drink

Pattern: Prototype

Description

It is used when the type of objects to create is determined by a prototypical instance, which is cloned to produce new objects

Example in .NET :

ICloneable 

 
using System;  
namespace Prototype; 
class Parent : ICloneable
{
    public int Age { get; set; }
    public Child MyChild { get; set; }

    public object Clone()
    {
        //TODO: serialize + unserialize 
        //with System.Text.Json.JsonSerializer

        var p = ShallowClone();
        //TODO: clone the child 
        var c = new Child();
        c.Age = this.MyChild.Age;

        p.MyChild = c;
        return p;
    }

    public Parent ShallowClone()
    {
        return this.MemberwiseClone() as Parent;
    }
}

Learn More

Wikipedia

Homework

Imagine that you have a cow farm and you want to create a new cow. Implement a prototype that will allow you to clone a cow. The cow should have a name and a weight

Friday Links 457

  1. Lazy Loading of Related Data – EF Core | Microsoft Learn
  2. Introducing the MSTest Runner – CLI, Visual Studio, & More – .NET Blog
  3. Quickly create your first prompt in Semantic Kernel | Microsoft Learn
  4. We need to talk about digital ownership
  5. Should you Stay Technical as an Engineering Manager?
  6. Aaron Schlesinger’s Personal Site
  7. ByronMayne/SourceGenerator.Foundations: A Source Generator for Source Generators. Gives out of the box support for transistent dependencies and logging right in Visual Studio

Pattern: Singleton

Description

Singleton pattern restricts the instantiation of a class to one object. It is used when you want to have one instance of a class that is shared across the application.

Example in .NET :

Singleton 

 
using System.Data.OleDb;

namespace Singleton;
/// <summary>
/// 
///sealed class Singleton
///{
///    private Singleton() { }
///    public static readonly Singleton Instance = new Singleton();
///}
///
/// </summary>
internal class SingletonDemo
{
    public static void GetFactory()
    {
        //cannot do new
        //OleDbFactory factory=new OleDbFactory();
        //get singleton instance
        OleDbFactory factory = OleDbFactory.Instance;
    }
}

Learn More

Wikipedia

Homework

Implement a singleton that will allow you to create a single instance of a logger that logs to a file and to a console.

Pattern: Strategy

Description

Strategy pattern allows a client to choose from a family of algorithms at runtime. It is used when the client expects to have multiple algorithms and wants to choose one of them at runtime.

Example in .NET :

Strategy 

using System;
using System.Collections.Generic;

namespace Strategy;
internal class StrategyDemo
{
    public static void SortWithDifferentStrategies()
    {
        List<int> al = new ();
        al.Add(102);
        al.Add(201);
        //sort ascending
        al.Sort((x, y) =&gt; x.CompareTo(y));

        for (int i = 0; i &lt; al.Count; i++)
        {
            Console.WriteLine(al[i]);
        }

        Console.WriteLine("---------------");

        //sort descending
        al.Sort((y, x) =&gt; x.CompareTo(y));
        for (int i = 0; i &lt; al.Count; i++)
        {
            Console.WriteLine(al[i]);
        }
        Console.WriteLine("---------------");
        //sort custom
        al.Sort((x, y) =&gt; LastDigit(x).CompareTo(LastDigit(y)));
        for (int i = 0; i &lt; al.Count; i++)
        {
            Console.WriteLine(al[i]);
        }

        var array = al.FindAll(it =&gt; it &gt; 10);


    }

    static int LastDigit(int x)
    {
        return x % 10;
    }

}

Learn More

Wikipedia

Homework

Image you want to serialize classes to XML,JSON and CSV . Implement a strategy that will allow you to choose between XML , JSON and CSV serialization at runtime.

Pattern: Visitor

Description

Visitor pattern is a way of separating an algorithm from an object structure on which it operates. A practical result of this separation is the ability to add new operations to existing object structures without modifying the structures.

Example in .NET :

Visitor 

using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;

namespace Visitor;
internal class VisitorDemo
{
    public static void VisitMethods()
    {
        var Code = @"""
using System;
namespace Test1
{
    class Program
    {
        static void Main(string[] args)
        {
              var dt=DateTime.Now;
			  Console.WriteLine(dt);
        }
     }
}

""";
        var tree = CSharpSyntaxTree.ParseText(Code);

        var node = tree.GetRoot();

        MethodVisiting LG = new MethodVisiting();
        //start visiting
        var sn = LG.Visit(node);

    }
}
public class MethodVisiting : CSharpSyntaxRewriter
{
    public override SyntaxNode? VisitMethodDeclaration(MethodDeclarationSyntax node)
    {
        if (node.Body == null || node.Body.Statements.Count == 0)
            return base.VisitMethodDeclaration(node);

        var parent = node.Parent as ClassDeclarationSyntax;
        
        if (parent == null)
            return base.VisitMethodDeclaration(node);

        var nameMethod = node.Identifier.Text;
        var nameClass = parent.Identifier.Text;
        Console.WriteLine($"visiting {nameMethod} from {nameClass}");

        return base.VisitMethodDeclaration(node);

    }
}

Learn More

Wikipedia

Homework

Implement a visitor that will allow you to calculate the total price of a shopping cart. The shopping cart should contain items with a price and a quantity.Visit every item and make the sum

Friday Links 456

  1. People Don’t Understand OOP – Sigma’s Blog
  2. Blazor RenderFragment – How To Use Plugins To Generate HTML
  3. Free your HTTP API. Misconceptions are holding you back! – CodeOpinion
  4. dnSpy/dnSpy: .NET debugger and assembly editor
  5. MegaLinter by OX Security
  6. GitHub – jordan-cutler/path-to-senior-engineer-handbook: All the resources you need to get to Senior Engineer and beyond
  7. Software Development and Postmortems
  8. GitHub – danluu/post-mortems: A collection of postmortems. Sorry for the delay in merging PRs!
  9. Getting Started – Vocs
  10. I thought software subscriptions were a ripoff until I did the math | ZDNET

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