switch

普通の switch

reg_switch.d

import std.stdio;
import std.string;

void main(){
  write("Enter Y/N > ");

  char [] s = readln().dup;
  s = chomp(s.idup).dup;

  switch(s){
/*
  switch 文は整数だけじゃなく文字列も使えてハッピー
*/
  case "y", "Y", "yes":
/*
  case 文にはカンマで区切って複数の値を指定可能
*/
    writeln("Yes"); break;
/*
  fall through するので break は必要
*/
  case "n", "N", "no":
    writeln("No"); break;
  default:
    writeln("...?");
/*
  D 言語では default がないと該当する case がないときに
  実行時にエラーになるのでちゃんと書くべき.
*/
  }
}

reg_switch.d の実行結果は:

[cactus:~/code_d/d_tuts]% ./reg_switch
Enter Y/N > y
Yes
[cactus:~/code_d/d_tuts]% ./reg_switch
Enter Y/N > Y
Yes
[cactus:~/code_d/d_tuts]% ./reg_switch
Enter Y/N > n
No
[cactus:~/code_d/d_tuts]% ./reg_switch
Enter Y/N > N
No

final switch

final_switch.d

import std.stdio;

enum Color{ RED, YELLOW, GREEN}

void main(){
  int i;
  Color c = Color.RED;
  
  while(i < 9){
    final switch(c){
    case Color.RED:
      c = Color.YELLOW;
      writeln("SIGNAL is YELLOW");
      break;
    case Color.YELLOW:
      c = Color.GREEN;
      writeln("SIGNAL is GREEN");
      break;
    case Color.GREEN:
      c = Color.RED;
      writeln("SIGNAL is RED");
      break;
/*
  final switch には default は書けない.
*/
    }
    i++;
  }
}

final_switch.d の実行結果は:

[cactus:~/code_d/d_tuts]% ./final_switch
SIGNAL is YELLOW
SIGNAL is GREEN
SIGNAL is RED
SIGNAL is YELLOW
SIGNAL is GREEN
SIGNAL is RED
SIGNAL is YELLOW
SIGNAL is GREEN
SIGNAL is RED