[Dart] 조건문

개요

• switch
  • 표현식
    • 함수처럼 사용하여 값을 반환
  • 패턴 매칭
    • 복잡한 조건 사용 가능
  • 엄격한 검사
    • 코드가 입력 받을 수 있는 모든 조건을 전부 확인하고 있는지 검사
  • 보호 구문
    • when 키워드로 보호 구문 추가
    • when 키워드는 boolean으로 반환할 조건을 각 case문에 추가
    • when 키워드 뒤에 오는 조건이 true를 반환하지 않으면 case 매치가 되지 않음

예제

• 코드

  • void if_test() {
      print('--- start if_test ---');
           
      int i = 1;
      if (i == 1) {
        print(1);
      } else if (i == 2) {
        print(2);
      } else {
        print('else');
      }
           
      print('--- end if_test ---\n');
    }
           
    void switch_test() {
      print('--- start switch_test ---');
      int i = 1;
      switch (i) {
        case 1:
          print(1);
          break;
        case 2:
          print(2);
          break;
        default:
          print('default');
          break;
      }
           
      print('--- end switch_test ---\n');
    }
           
    void switch_expression_test() {
      print('--- start switch_expression_test ---');
           
      int i = 1;
           
      String s = switch (i) {
        1 => '1',
        2 => '2',
        3 => '3',
        _ => '_',
      };
           
      print(s);
           
      print('--- end switch_expression_test ---\n');
    }
           
    void switch_pattern_matching_test(dynamic any) {
      print('--- start switch_pattern_matching_test ---');
           
      switch (any) {
        case 1:
          print(1);
          break;
        case [1, 2]:
          print('[1, 2]');
          break;
        case [_, _, _]:
          print('[_, _, _]');
          break;
        case [int i, String s]:
          print('[int i, String s]');
          break;
        case (int i, String s):
          print('(int i, String s)');
          break;
        default:
          print('default');
          break;
      }
           
      print('--- end switch_pattern_matching_test ---\n');
    }
           
    void switch_exhaustiveness_checking_test() {
      print('--- start switch_exhaustiveness_checking_test ---');
           
      bool? b;
           
      switch (b) {
        case true:
          print('true');
          break;
        case false:
          print('false');
          break;
        case null:
          print('null');
          break;
      }
           
      print('--- end switch_exhaustiveness_checking_test ---\n');
    }
           
    void switch_guard_clause_test() {
      print('--- start switch_guard_clause_test ---');
           
      (int i, int j) value = (1, 2);
           
      switch (value) {
        case (_, _) when value.$1 == 1:
          print(1);
          break;
        default:
          print('default');
      }
           
      print('--- end switch_guard_clause_test ---\n');
    }
           
    void main() async {
      if_test();
           
      switch_test();
           
      switch_expression_test();
           
      switch_pattern_matching_test(1);
      switch_pattern_matching_test([1, 2]);
      switch_pattern_matching_test([1, 2, 3]);
      switch_pattern_matching_test([1, 'a']);
      switch_pattern_matching_test((1, 'a'));
      switch_pattern_matching_test((1, 'a', 3));
           
      switch_exhaustiveness_checking_test();
           
      switch_guard_clause_test();
    }
    

• 실행 결과

  • --- start if_test ---
    1
    --- end if_test ---
           
    --- start switch_test ---
    1
    --- end switch_test ---
           
    --- start switch_expression_test ---
    1
    --- end switch_expression_test ---
           
    --- start switch_pattern_matching_test ---
    1
    --- end switch_pattern_matching_test ---
           
    --- start switch_pattern_matching_test ---
    [1, 2]
    --- end switch_pattern_matching_test ---
           
    --- start switch_pattern_matching_test ---
    [_, _, _]
    --- end switch_pattern_matching_test ---
           
    --- start switch_pattern_matching_test ---
    [int i, String s]
    --- end switch_pattern_matching_test ---
           
    --- start switch_pattern_matching_test ---
    (int i, String s)
    --- end switch_pattern_matching_test ---
           
    --- start switch_pattern_matching_test ---
    default
    --- end switch_pattern_matching_test ---
           
    --- start switch_exhaustiveness_checking_test ---
    null
    --- end switch_exhaustiveness_checking_test ---
           
    --- start switch_guard_clause_test ---
    1
    --- end switch_guard_clause_test ---