LanguageFeatures/Patterns/switch_expression_A03_t12.dart

// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

/// @assertion
/// primary                 ::= // Existing productions...
///                           | switchExpression
///
/// switchExpression      ::= 'switch' '(' expression ')' '{'
///                           switchExpressionCase ( ',' switchExpressionCase )*
///                           ','? '}'
/// switchExpressionCase  ::= guardedPattern '=>' expression
///
/// The body is a series of cases. Each case has a pattern, optional guard, and
/// a single expression body. As with other expression forms containing a list
/// of subelements (argument lists, collection literals), the cases are
/// separated by commas with an optional trailing comma. Since the body of each
/// case is a single expression with a known terminator, it's easy to tell when
/// one case ends and the next begins. That lets us do away with the case
/// keyword.
///
/// To keep the syntax small and light, we also disallow a default clause.
/// Instead, you can use a shorter _ wildcard pattern to catch any remaining
/// values.
///
/// Slotting into primary means it can be used anywhere any expression can
/// appear, even as operands to unary and binary operators. Many of these uses
/// are ugly, but not any more problematic than using a collection literal in
/// the same context since a switch expression is always delimited by a switch
/// and }.
///
/// @description Check that a switch expression can be used as operand of
/// cascade operator
/// @author sgrekhov22@gmail.com

import "../../Utils/expect.dart";

String log = "";

abstract class A {
  void foo();
  void bar();
}

class B extends A {
  void foo() {
    log += "B.foo();";
  }
  void bar() {
    log += "B.bar();";
  }
}

class C extends A {
  void foo() {
    log += "C.foo();";
  }
  void bar() {
    log += "C.bar();";
  }
}

A test(String s) =>
  switch(s) {
    "b" => B(),
    _ => C()
  } .. foo()
    .. bar();

main() {
  var x = test("b");
  Expect.isTrue(x is B);
  Expect.equals("B.foo();B.bar();", log);
  log = "";
  var y = test("c");
  Expect.isTrue(y is C);
  Expect.equals("C.foo();C.bar();", log);
}