Chapter05.dib

#!markdown

# Chapter 5 - Building Your Own Types with Object-Oriented Programming

Execute the following code cell to make `Console` methods available in every code cell in this notebook.

We cannot create a class library in a .NET Interactive notebook so we will put all code in the same notebook.

#!csharp

using static System.Console;

using System.Collections.Generic;

#!markdown

## Storing a value using an enum type (defining the enum)

#!csharp

[System.Flags]
public enum WondersOfTheAncientWorld : byte
{
  None = 0b_0000_0000, // i.e. 0
  GreatPyramidOfGiza = 0b_0000_0001, // i.e. 1
  HangingGardensOfBabylon = 0b_0000_0010, // i.e. 2
  StatueOfZeusAtOlympia = 0b_0000_0100, // i.e. 4
  TempleOfArtemisAtEphesus = 0b_0000_1000, // i.e. 8
  MausoleumAtHalicarnassus = 0b_0001_0000, // i.e. 16
  ColossusOfRhodes = 0b_0010_0000, // i.e. 32
  LighthouseOfAlexandria = 0b_0100_0000  // i.e. 64
}

#!markdown

## Defining a class

.NET Interactive notebooks do not support namespaces. You would get a "Cannot declare namesapce in script code" error. But we can declare a class.

#!markdown

## Storing a value using an enum type (using the enum)

#!csharp

public class Person : object
{
  // fields
  public string Name;
  public DateTime DateOfBirth;
  public WondersOfTheAncientWorld FavoriteAncientWonder;
  public WondersOfTheAncientWorld BucketList;
  public List<Person> Children = new();

  // constants
  public const string Species = "Homo Sapien";

  // read-only fields
  public readonly string HomePlanet = "Earth";
  public readonly DateTime Instantiated;

  // constructors
  public Person()
  {
    // set default values for fields
    // including read-only fields
    Name = "Unknown"; 
    Instantiated = DateTime.Now;
  }

  public Person(string initialName, string homePlanet)
  {
    Name = initialName;
    HomePlanet = homePlanet;
    Instantiated = DateTime.Now;
  }

  // methods
  public void WriteToConsole()
  {
    WriteLine($"{Name} was born on a {DateOfBirth:dddd}.");
  }

  public string GetOrigin()
  {
    return $"{Name} was born on {HomePlanet}.";
  }

  public (string, int) GetFruit()
  {
    return ("Apples", 5);
  }

  public (string Name, int Number) GetNamedFruit()
  {
    return (Name: "Apples", Number: 5);
  }

  public string SayHello()
  {
    return $"{Name} says 'Hello!'";
  }

  public string SayHello(string name)
  {
    return $"{Name} says 'Hello {name}!'";
  }

  public string OptionalParameters(
    string command = "Run!",
    double number = 0.0,
    bool active = true)
  {
    return string.Format(
    format: "command is {0}, number is {1}, active is {2}",
    arg0: command,
    arg1: number,
    arg2: active);
  }

  public void PassingParameters(int x, ref int y, out int z)
  {
    // out parameters cannot have a default
    // AND must be initialized inside the method
    z = 99;
    // increment each parameter
    x++;
    y++;
    z++;
  }

  // a property defined using C# 1 - 5 syntax
  public string Origin
  {
    get
    {
    return $"{Name} was born on {HomePlanet}";
    }
  }

  // two properties defined using C# 6+ lambda expression body syntax
  public string Greeting => $"{Name} says 'Hello!'";
  
  public int Age => System.DateTime.Today.Year - DateOfBirth.Year;

  public string FavoriteIceCream { get; set; } // auto-syntax

  private string favoritePrimaryColor;
  public string FavoritePrimaryColor
  {
    get
    {
      return favoritePrimaryColor;
    }
    set
    {
      switch (value.ToLower())
      {
        case "red":
        case "green":
        case "blue":
          favoritePrimaryColor = value;
          break;
        default:
          throw new System.ArgumentException(
            $"{value} is not a primary color. " +
            "Choose from: red, green, blue.");
      }
    }
  }

  // indexers
  public Person this[int index]
  {
    get
    {
      return Children[index]; // pass on to the List<T> indexer
    }
    set
    {
      Children[index] = value;
    }
  }

  // end of class
}

#!markdown

## Instantiating a class

The namespace for a class defined in a .NET Interactive notebook follows the pattern `Submission#[number]+[classname]`.

#!csharp

// Person bob = new Person(); // C# 1.0 or later
// var bob = new Person(); // C# 3.0 or later
Person bob = new(); // C# 9.0 or later
WriteLine(bob.ToString());

bob.Name = "Bob Smith";
bob.DateOfBirth = new DateTime(1965, 12, 22); // C# 1.0 or later

WriteLine(format: "{0} was born on {1:dddd, d MMMM yyyy}", 
  arg0: bob.Name,
  arg1: bob.DateOfBirth);

Person alice = new()
{
  Name = "Alice Jones",
  DateOfBirth = new(1998, 3, 7) // C# 9.0 or later
};

WriteLine(format: "{0} was born on {1:dd MMM yy}",
  arg0: alice.Name,
  arg1: alice.DateOfBirth);

#!csharp

bob.FavoriteAncientWonder = WondersOfTheAncientWorld.StatueOfZeusAtOlympia;

WriteLine(
  format: "{0}'s favorite wonder is {1}. Its integer is {2}.",
  arg0: bob.Name,
  arg1:  bob.FavoriteAncientWonder,
  arg2: (int)bob.FavoriteAncientWonder);

bob.BucketList = 
  WondersOfTheAncientWorld.HangingGardensOfBabylon
  | WondersOfTheAncientWorld.MausoleumAtHalicarnassus;

// bob.BucketList = (WondersOfTheAncientWorld)18;

WriteLine($"{bob.Name}'s bucket list is {bob.BucketList}");

#!markdown

## Storing multiple values using collections

#!csharp

bob.Children.Add(new Person { Name = "Alfred" }); 
bob.Children.Add(new Person { Name = "Zoe" });

WriteLine(
  $"{bob.Name} has {bob.Children.Count} children:");

for (int childIndex = 0; childIndex < bob.Children.Count; childIndex++)
{
  WriteLine($"  {bob.Children[childIndex].Name}");
}

#!markdown

## Making a field static

#!csharp

public class BankAccount
{
  public string AccountName; // instance member
  public decimal Balance; // instance member
  public static decimal InterestRate; // shared member
}

#!csharp

BankAccount.InterestRate = 0.012M; // store a shared value

var jonesAccount = new BankAccount(); 
jonesAccount.AccountName = "Mrs. Jones"; 
jonesAccount.Balance = 2400;

WriteLine(format: "{0} earned {1:C} interest.",
  arg0: jonesAccount.AccountName,
  arg1: jonesAccount.Balance * BankAccount.InterestRate);

var gerrierAccount = new BankAccount(); 
gerrierAccount.AccountName = "Ms. Gerrier"; 
gerrierAccount.Balance = 98;

WriteLine(format: "{0} earned {1:C} interest.",
  arg0: gerrierAccount.AccountName,
  arg1: gerrierAccount.Balance * BankAccount.InterestRate);

#!markdown

## Making a field constant

#!csharp

WriteLine($"{bob.Name} is a {Person.Species}");

#!markdown

## Making a field read-only

#!csharp

WriteLine($"{bob.Name} was born on {bob.HomePlanet}");

#!markdown

## Initializing fields with constructors

#!csharp

var blankPerson = new Person();

WriteLine(format:
  "{0} of {1} was created at {2:hh:mm:ss} on a {2:dddd}.",
  arg0: blankPerson.Name,
  arg1: blankPerson.HomePlanet,
  arg2: blankPerson.Instantiated);

#!markdown

## Defining multiple constructors

#!csharp

var gunny = new Person("Gunny", "Mars");

WriteLine(format:
  "{0} of {1} was created at {2:hh:mm:ss} on a {2:dddd}.",
  arg0: gunny.Name,
  arg1: gunny.HomePlanet,
  arg2: gunny.Instantiated);

#!markdown

## Returning values from methods

#!csharp

bob.WriteToConsole(); 
WriteLine(bob.GetOrigin());

#!markdown

## Combining multiple returned values using tuples

#!csharp

public class TextAndNumber
{
  public string Text;
  public int Number;
}

public class LifeTheUniverseAndEverything
{
  public TextAndNumber GetTheData()
  {
    return new TextAndNumber
    {
      Text = "What's the meaning of life?",
      Number = 42
    };
  }
}

#!markdown

### Language support for tuples

#!csharp

(string, int) fruit = bob.GetFruit();

WriteLine($"{fruit.Item1}, {fruit.Item2} there are.");

#!markdown

### Naming the fields of a tuple

#!csharp

var fruitNamed = bob.GetNamedFruit();

WriteLine($"There are {fruitNamed.Number} {fruitNamed.Name}.");

#!markdown

### Inferring tuple names

#!csharp

var thing1 = ("Neville", 4);
WriteLine($"{thing1.Item1} has {thing1.Item2} children.");

var thing2 = (bob.Name, bob.Children.Count); 
WriteLine($"{thing2.Name} has {thing2.Count} children.");

#!markdown

### Deconstructing tuples

#!csharp

(string fruitName, int fruitNumber) = bob.GetFruit();

WriteLine($"Deconstructed: {fruitName}, {fruitNumber}");

#!markdown

## Defining and passing parameters to methods

#!csharp

WriteLine(bob.SayHello());
WriteLine(bob.SayHello("Emily"));

#!markdown

## Passing optional and named parameters

#!csharp

WriteLine(bob.OptionalParameters());

#!csharp

WriteLine(bob.OptionalParameters("Jump!", 98.5));

#!csharp

WriteLine(bob.OptionalParameters(
  number: 52.7, command: "Hide!"));

#!csharp

WriteLine(bob.OptionalParameters("Poke!", active: false));

#!markdown

## Controlling how parameters are passed

When a parameter is passed into a method, it can be passed in one of three ways:
- By value (this is the default): Think of these as being in-only.
- By reference as a ref parameter: Think of these as being in-and-out.
- As an out parameter: Think of these as being out-only.

#!csharp

int a = 10;
int b = 20;
int c = 30;

WriteLine($"Before: a = {a}, b = {b}, c = {c}");
bob.PassingParameters(a, ref b, out c);
WriteLine($"After: a = {a}, b = {b}, c = {c}");

#!markdown

## Simplified out parameters

In C# 7.0 and later, we can simplify code that uses the out variables.

#!csharp

int d = 10;
int e = 20;

WriteLine($"Before: d = {d}, e = {e}, f doesn't exist yet!");

// simplified C# 7.0 or later syntax for the out parameter
bob.PassingParameters(d, ref e, out int f);
WriteLine($"After: d = {d}, e = {e}, f = {f}");

#!markdown

# Splitting classes using partial

Partial classes are not supported in .NET Interactive notebooks. I have added the code to the original class near the top of this notebook. 

#!csharp

Person sam = new()
{
  Name = "Sam",
  DateOfBirth = new(1972, 1, 27)
};
WriteLine(sam.Origin);
WriteLine(sam.Greeting);
WriteLine(sam.Age);

#!csharp

sam.FavoriteIceCream = "Chocolate Fudge";

WriteLine($"Sam's favorite ice-cream flavor is {sam.FavoriteIceCream}.");

sam.FavoritePrimaryColor = "Red";

WriteLine($"Sam's favorite primary color is {sam.FavoritePrimaryColor}.");

#!markdown

# Defining indexers

#!csharp

sam.Children.Add(new() { Name = "Charlie" });
sam.Children.Add(new() { Name = "Ella" });

WriteLine($"Sam's first child is {sam.Children[0].Name}");
WriteLine($"Sam's second child is {sam.Children[1].Name}");

WriteLine($"Sam's first child is {sam[0].Name}");
WriteLine($"Sam's second child is {sam[1].Name}");

#!markdown

# Pattern matching with objects

#!csharp

public class BusinessClassPassenger
{
  public override string ToString()
  {
    return $"Business Class";
  }
}

public class FirstClassPassenger
{
  public int AirMiles { get; set; }

  public override string ToString()
  {
    return $"First Class with {AirMiles:N0} air miles";
  }
}

public class CoachClassPassenger
{
  public double CarryOnKG { get; set; }

  public override string ToString()
  {
    return $"Coach Class with {CarryOnKG:N2} KG carry on";
  }
}

#!csharp

object[] passengers = {
  new FirstClassPassenger { AirMiles = 1_419 },
  new FirstClassPassenger { AirMiles = 16_562 },
  new BusinessClassPassenger(),
  new CoachClassPassenger { CarryOnKG = 25.7 },
  new CoachClassPassenger { CarryOnKG = 0 },
};

foreach (object passenger in passengers)
{
  decimal flightCost = passenger switch
  {
    /*
    FirstClassPassenger p when p.AirMiles > 35000 => 1500M,
    FirstClassPassenger p when p.AirMiles > 15000 => 1750M,
    FirstClassPassenger _                         => 2000M, */

    // C# 9 or later syntax
    FirstClassPassenger p => p.AirMiles switch
    {
      > 35000 => 1500M,
      > 15000 => 1750M,
      _       => 2000M
    },


    BusinessClassPassenger                        => 1000M,
    CoachClassPassenger p when p.CarryOnKG < 10.0 => 500M,
    CoachClassPassenger                           => 650M,
    _                                             => 800M
  };

  WriteLine($"Flight costs {flightCost:C} for {passenger}");
}

#!markdown

# Working with records

#!markdown

## Init-only properties

#!csharp

#nullable enable

public class ImmutablePerson
{
  public string? FirstName { get; init; }
  public string? LastName { get; init; }
}

#!csharp

ImmutablePerson jeff = new()
{
  FirstName = "Jeff",
  LastName = "Winger"
};
jeff.FirstName = "Geoff";

#!markdown

## Understanding records

#!csharp

#nullable enable

public record ImmutableVehicle
{
  public int Wheels { get; init; }
  public string? Color { get; init; }
  public string? Brand { get; init; }
}

#!csharp

ImmutableVehicle car = new()
{
  Brand = "Mazda MX-5 RF",
  Color = "Soul Red Crystal Metallic",
  Wheels = 4
};

ImmutableVehicle repaintedCar = car
  with { Color = "Polymetal Grey Metallic" };

  WriteLine($"Original car color was {car.Color}.");
WriteLine($"New car color is {repaintedCar.Color}.");

#!markdown

## Simplifying data members in records

#!csharp

// simpler way to define a record
// auto-generates the properties, constructor, and deconstructor
public record ImmutableAnimal(string Name, string Species);

#!csharp

ImmutableAnimal oscar = new("Oscar", "Labrador");
var (who, what) = oscar; // calls Deconstruct method
WriteLine($"{who} is a {what}.");