Proposed pattern matching in C#

csharp7-switch.cs

// From: https://blogs.msdn.microsoft.com/dotnet/2016/08/24/whats-new-in-csharp-7-0/

switch(shape)
{
    case Circle c:
        WriteLine($"circle with radius {c.Radius}");
        break;
    case Rectangle s when (s.Length == s.Height):
        WriteLine($"{s.Length} x {s.Height} square");
        break;
    case Rectangle r:
        WriteLine($"{r.Length} x {r.Height} rectangle");
        break;
    default:
        WriteLine("<unknown shape>");
        break;
    case null:
        throw new ArgumentNullException(nameof(shape));
}

proposed-match.cs

match (shape)
{
    Circle c => WriteLine($"circle with radius {c.Radius}");
    Rectangle s when (s.Length == s.Height) { //statement block example
        WriteLine($"{s.Length} x {s.Height} square"); 
    }
    Rectangle r => WriteLine($"{r.Length} x {r.Height} rectangle");
    default => WriteLine("<unknown shape>");
    null => throw new ArgumentNullException(nameof(shape));
}