switch

Summary#

switch (scrutinee) { … } branches on a value against constant case labels, running the first matching section (or default if none match). Only the matched section runs — there is no implicit fall-through — so a trailing break is idiomatic but optional. break exits the switch; continue inside a switch continues the enclosing loop.

Signature#

switch (<scrutinee>) {
  case <const>:
  case <const>:      // stacked labels share a body
    <statements>
    break;           // optional — sections never fall through
  default:
    <statements>
}

Description#

• Case labels are compile-time constants — literals, enum members, or consts — comparable to the scrutinee's type (int, string, enum, bool). A non-constant or type-incompatible label is a compile error.
• Stacked labels (case 1: case 2:) share one body.
• default runs when no case matches; at most one is allowed, and it may appear anywhere.
• No fall-through: only the matched section runs, then the switch exits. A trailing break is accepted (and idiomatic) but not required — unlike C#, Osy# sections never fall through, so a missing break is not an error.
• break exits the switch (it is a break boundary, not a loop). continue inside a switch that sits in a loop continues that loop (it passes through the switch) — exactly C#.
• A function whose value is produced entirely by a switch needs an exhaustive switch (a default where every section returns) to satisfy definite-return.
• Durable: a suspend inside a case body survives serialize/restore.

Examples#

string Grade(int score) {
  switch (score) {
    case 5: case 4: return "pass";     // stacked labels
    case 3: return "marginal";
    default: return "fail";
  }
}

int Code(string s) {
  switch (s) {                          // switch on a string
    case "red": return 1;
    case "green": return 2;
    default: return 0;
  }
}

// break exits the SWITCH, not the loop; continue continues the LOOP.
int Scan(int[] xs) {
  int total = 0;
  for (int i = 0; i < xs.Length; i++) {
    switch (xs[i]) {
      case 0: continue;                 // skip zeros — continues the for loop
      default: break;                   // exits the switch, falls to the += below
    }
    total = total + xs[i];
  }
  return total;
}

See also#

• if / else — the two-way / chained conditional
• break / continue — how break and continue behave in loops vs switch
• for — the loop continue targets when inside a switch