C# Language Trick – Pattern Matching

if (shape is Circle c) { /* ... */ }
else if (shape is Rectangle r) { /* ... */ }
else if (shape is Triangle t) { /* ... */ }

var area = shape switch
{
    Circle c => Math.PI * c.Radius * c.Radius,
    Rectangle r => r.Width * r.Height,
    Triangle t => t.Base * t.Height / 2,
    _ => throw new ArgumentException("Unknown shape")
};