C# 8: Pattern Matching Extended

2018-07-04T03:01:08+02:00

Examples?

2018-07-04T07:03:46+02:00

Greetings,
Christian

	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}";
	default:
	return "another shape";
	}
	}

	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);

	public string Name => GetType().Name;
	}

	static void Main()
	{
	var r1 = new Rectangle(position: (200, 200), size: (200, 200));
	var e1 = new Ellipse(position: (80, 1400), size: (80, 140));
	var shapes = new Shape[]
	{
	r1,
	e1,
	new Circle((40, 60), 90),
	new CombinedShape(r1, e1)
	};

	foreach (var shape in shapes)
	{
	Console.WriteLine(M1(shape));
	}
	}

	static string M2(Shape shape)
	=> shape switch
	{
	Shape s when s.Size.height > 100 => $"large shape with size {s.Size} at position {s.Position}",
	Ellipse e => $"Ellipse with size {e.Size} at position {e.Position}",
	Rectangle r => $"Rectangle with size {r.Size} at position {r.Position}",
	_ => "another shape"
	};

	static string M3(Shape shape)
	=> shape switch
	{
	CombinedShape (var shape1, var (pos, _)) => $"combined shape – shape1: {shape1.Name}, pos of shape2: {pos}",
	{ Size: (200, 200), Position: var pos } => $"shape with size 200×200 at position {pos.x}:{pos.y}",
	Ellipse (var pos, var size) => $"Ellipse with size {size} at position {pos}",
	Rectangle (_, var size) => $"Rectangle with size {size}",
	_ => "another shape"
	};

Pattern Matching with the switch Statement