Switch and case

Switch statements in Dart compare integer, string, or compile-timeconstants using ==. The compared objects must all be instances of thesame class (and not of any of its subtypes), and the class must notoverride ==.Enumerated types work well in switch statements.

Note: Switch statements in Dart are intended for limited circumstances, such as in interpreters or scanners.

Each non-empty case clause ends with a break statement, as a rule.Other valid ways to end a non-empty case clause are a continue,throw, or return statement.

Use a default clause to execute code when no case clause matches:

  1. var command = 'OPEN';
  2. switch (command) {
  3.   case 'CLOSED':
  4.     executeClosed();
  5.     break;
  6.   case 'PENDING':
  7.     executePending();
  8.     break;
  9.   case 'APPROVED':
  10.     executeApproved();
  11.     break;
  12.   case 'DENIED':
  13.     executeDenied();
  14.     break;
  15.   case 'OPEN':
  16.     executeOpen();
  17.     break;
  18.   default:
  19.     executeUnknown();
  20. }

The following example omits the break statement in a case clause,thus generating an error:

  1. var command = 'OPEN';
  2. switch (command) {
  3.   case 'OPEN':
  4.     executeOpen();
  5.     // ERROR: Missing break
  7.   case 'CLOSED':
  8.     executeClosed();
  9.     break;
  10. }

However, Dart does support empty case clauses, allowing a form offall-through:

  1. var command = 'CLOSED';
  2. switch (command) {
  3.   case 'CLOSED': // Empty case falls through.
  4.   case 'NOW_CLOSED':
  5.     // Runs for both CLOSED and NOW_CLOSED.
  6.     executeNowClosed();
  7.     break;
  8. }

If you really want fall-through, you can use a continue statement anda label:

  1. var command = 'CLOSED';
  2. switch (command) {
  3.   case 'CLOSED':
  4.     executeClosed();
  5.     continue nowClosed;
  6.   // Continues executing at the nowClosed label.
  8.   nowClosed:
  9.   case 'NOW_CLOSED':
  10.     // Runs for both CLOSED and NOW_CLOSED.
  11.     executeNowClosed();
  12.     break;
  13. }

A case clause can have local variables, which are visible only insidethe scope of that clause.