Switch Syntax

switch branches on enum variants, literals, null, or nominal runtime types. Each case uses a block; its expression form produces a result through break value.

String text = switch token {
    case Number(Double value) { break "number" }
    case Name(String value) { break value }
    case End { break "end" }
}

Match order

The matched expression is evaluated once. Cases are tested in source order, and only the first matching case executes. There is no fallthrough. See pattern matching for complete pattern rules.

Exhaustiveness

Every switch must be exhaustive. The compiler computes coverage recursively from static types and patterns: a closed enum must cover every variant, a nullable type must cover null, and open nominal types or value domains that cannot be finitely enumerated must cover remaining values with _. A missing branch is a compile error.

An open type hierarchy cannot enumerate every subclass statically and needs an explicit fallback:

String kind = switch shape {
    case Circle circle { break "circle" }
    case _ { break "other" }
}

_ covers all unmatched values of the current type. A branch already completely covered by earlier patterns is unreachable and causes a compile error.

Completion rules

A statement switch case may complete normally, ending the whole switch. In an expression switch, each case path that can complete normally must execute break value. Abnormal paths such as return or throw need no local result. All break value results must merge into one static type.