christiannagel

public abstract class Shape
{
  public (int x, int y) Position { get; }
  public (int height, int width) Size { get; }
  
  public Shape((int x, int y) position, (int height, int width) size)
    => (Position, Size) = (position, size);

  public void Deconstruct(out (int x, int y) position, out (int x, int y) size)
    => (position, size) = (Position, Size);

christiannagel

static string M1(Shape shape)
{
  switch (shape)
  {
    case Shape s when s.Size.height > 100:
      return $"large shape with size {s.Size} at position {s.Position}";
    case Ellipse e:
      return $"Ellipse with size {e.Size} at position {e.Position}";
    case Rectangle r:
      return $"Rectangle with size {r.Size} at position {r.Position}";

christiannagel

var glory = new NewAndGlory();
string s1 = glory.GetANullString();
string s2 = glory.GetAString();
string s3 = glory.PassAString(null);  // having a NullReferenceException here!

christiannagel

static string GetIsbn1(Book book)
{
  string? isbn = book.Isbn;
  if (isbn == null)
  {
    return string.Empty;
  }
  return isbn;
}

christiannagel

public string GetIsbn2(Book book)
  => book.Isbn ?? string.Empty;

christiannagel

class SomeClass : ILegacyInterface
{
  public string? Foo() => null;
}

class AnotherClass : ILegacyInterface
{
  public string Foo() => "a string";
}

christiannagel

var newglory = new NewAndGlory();
string? s1 = newglory.GetANullString();
string s2 = newglory.GetAString();
// string s3 = newglory.PassAString(null); // error: cannot convert null literal to non-nullable reference or unconstrained type parameter

var old = new Legacy();
string s4 = old.GetANullString();  // no error, s1 is null!
string s5 = old.PassAString(null); // no error

christiannagel

class Book
{
  public string Title { get; }
  public string Publisher { get; }
  public string? Isbn { get; }
  public Book(string title, string publisher, string? isbn)
    => (Title, Publisher, Isbn) = (title, publisher, isbn);

  public Book(string title, string publisher)
    : this(title, publisher, null) { }

christiannagel

public class Legacy
{
  public string GetANullString() => null;
  public string PassAString(string s)
  {
    if (s == null) throw new ArgumentNullException(nameof(s));
    return s.ToUpper();
  }
}

christiannagel

{
  "version": "1.0",
  "defaultProvider": "cdnjs",
  "libraries": [
    {
      "library": "jquery@3.3.1",
      "destination": "wwwroot/lib/jQuery",
      "files": ["jquery.js", "jquery.min.js", "jquery.min.map"]
    }
  ]