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switch / patterns

By · Reviewed & last updated · Part of C# Tutorial

C# 8’s switch EXPRESSIONS are the modern default. They return a value, never fall through, and combine with patterns to replace big if chains with declarative dispatch.

Switch expression + property patterns

EXAMPLE
// 1) Basic switch expression
string describe = day switch {
    "Sat" or "Sun"                              => "weekend",
    "Mon" or "Tue" or "Wed" or "Thu" or "Fri"   => "weekday",
    _                                              => "unknown",
};

// 2) Type patterns + when clauses
string classify(object o) => o switch {
    int n when n > 0   => $"positive int {n}",
    int                 => "non-positive int",
    string { Length: 0 } => "empty string",
    string s             => $"string of {s.Length} chars",
    null                 => "null",
    _                    => "other",
};

// 3) Sealed-type exhaustiveness
public abstract record Shape;
public record Circle(double R)             : Shape;
public record Rect(double W, double H)     : Shape;
public record Triangle(double Base, double H) : Shape;

double Area(Shape s) => s switch {
    Circle c             => Math.PI * c.R * c.R,
    Rect r               => r.W * r.H,
    Triangle t           => 0.5 * t.Base * t.H,
    // compiler warns if you add a new Shape subtype and forget a case
};

// 4) Property patterns — destructure inside a case
public record Order(decimal Total, string Status, Customer Customer);
public record Customer(string Tier);

string fee(Order o) => o switch {
    { Status: "paid", Total:  > 1000, Customer.Tier: "gold" } => "VIP: 1%",
    { Status: "paid", Total:  > 100 }                         => "Std: 3%",
    { Status: "refunded" }                                     => "refund",
    _                                                            => "std",
};

Why it matters

Property patterns let you peek several levels deep without nesting ifs. Combine with sealed types or records and your business logic stops looking imperative.

Tip: Tweak the snippet with Try it Yourself », then sit the quiz at the bottom of the page.

Example

Example
string day = "SAT";
string kind = day switch {
    "SAT" or "SUN" => "weekend",
    _              => "weekday"
};
Console.WriteLine(kind);
Try it Yourself »

Discussion

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