Pattern matching: switch expression and property patterns for clean branching

Long if/else chains or switch statements with casting become verbose and error-prone when working with polymorphic types or complex conditions. Traditional approaches require explicit type checks and casts.

Use switch expressions with type, property, and relational patterns:

// Type pattern with property constraint
public string Describe(Shape shape) => shape switch
{
    Circle c when c.Radius > 10 => $"Large circle r={c.Radius}",
    Circle c                    => $"Small circle r={c.Radius}",
    Rectangle { Width: var w, Height: var h } when w == h => "Square",
    Rectangle r                 => $"Rectangle {r.Width}x{r.Height}",
    _                           => "Unknown shape"
};

// List pattern (C# 11)
string Classify(int[] arr) => arr switch
{
    []          => "empty",
    [var x]     => $"single: {x}",
    [var x, var y] => $"pair: {x},{y}",
    [.., > 100] => "ends with large number",
    _           => "other"
};

The compiler verifies exhaustiveness of switch expressions and emits a warning when not all cases are handled. Pattern matching compiles to efficient IL with type checks and direct field access — no reflection.