Switch expressions and patterns

The switch expression

A classic switch statement runs side effects; a switch expression evaluates to a value. You write the input, the keyword switch, then a brace-delimited list of pattern => result arms separated by commas. Arms are tested top to bottom and the first match wins, so order matters. The discard _ is the catch-all, and unlike a statement there is no fall-through and no break.

string label = day switch
{
    0 => "Sunday",
    6 => "Saturday",
    _ => "weekday",
};

Because it is an expression it composes anywhere a value is expected — a return, an interpolation, a method argument. The compiler also warns when the arms are not exhaustive, nudging you to handle every case.

Relational and logical patterns

Inside an arm you can match on a comparison rather than a constant. Relational patterns use <, <=, >, >= against a constant: > 0, <= 100. Logical patterns combine others with and, or, and not, with not binding tightest, then and, then or. This lets a single arm read like a range — >= 0 and < 60 — or exclude a value with not null. These compose with property and constant patterns too.

Tuple patterns and when guards

Wrap several values in parentheses and switch on the tuple to branch on a combination at once — (true, false), ("rock", "scissors"). Each position is itself a pattern, so you can mix constants, relational tests, and _ discards per slot.

When a pattern alone cannot express the condition — it needs to compare two inputs, call a method, or test an arbitrary boolean — add a when guard: a clause that runs only after the pattern matches and must also be true for the arm to win. Keep the pattern for shape and the guard for the leftover logic.