Use string Contains with switch

Question

I m doing an C  app where I use   if   message Contains  test          Console WriteLine  yes      else if   message Contains  test2          Console WriteLine  yes for test2        There would be any way to change to switch   the if   statements

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switch message      case  test       Console WriteLine  yes        break                    default      if  Contains  test2            Console WriteLine  yes for test2              break

User · Answer

If you just want to use switch case  you can do something like this  pseudo-code        string message    test of mine       string   keys   new string     test2     test           string sKeyResult   keys FirstOrDefault lt string gt  s  gt message Contains s         switch  sKeyResult                case  test               Console WriteLine  yes for test                break          case  test2               Console WriteLine  yes for test2                break          But if the quantity of keys is a big  you can just replace it with dictionary  like this    static Dictionary lt string  string gt  dict   new Dictionary lt string  string gt     static void Main string   args        string message    test of mine                 this happens only once  during initialization  this is just sample code     dict Add  test    yes        dict Add  test2    yes2           string sKeyResult   dict Keys FirstOrDefault lt string gt  s  gt message Contains s         Console WriteLine dict sKeyResult      or  TryGetValue

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Simple yet efficient with c   string sri    quot Naveen quot       switch  sri                case var s when sri Contains  quot ee quot               Console WriteLine  quot oops  worked    quot            break          case var s when sri Contains  quot same quot               Console WriteLine  quot oops  Not found    quot            break

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This will work in C  7  As of this writing  it has yet to be released  But if I understand this correctly  this code will work   switch message        case Contains  test            Console WriteLine  yes            break      case Contains  test2            Console WriteLine  yes for test2            break      default          Console WriteLine  No matches found         Source  https   blogs msdn microsoft com dotnet 2016 08 24 whats-new-in-csharp-7-0

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Some custom swtich can be created like this  Allows multiple case execution as well  public class ContainsSwitch        List lt ContainsSwitch gt  actionList   new List lt ContainsSwitch gt         public string Value   get  set        public Action Action   get  set        public bool SingleCaseExecution   get  set        public void Perform  string target                foreach  ContainsSwitch act in actionList                        if  target Contains act Value                                 act Action                    if SingleCaseExecution                      break                                    public void AddCase string value  Action act                actionList Add new ContainsSwitch     Action   act  Value   value               Call like this  string m    abc   ContainsSwitch switchAction   new ContainsSwitch    switchAction SingleCaseExecution   true  switchAction AddCase  a   delegate     Console WriteLine  matched a        switchAction AddCase  d   delegate     Console WriteLine  matched d        switchAction AddCase  a   delegate     Console WriteLine  matched a         switchAction Perform m

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Faced with this issue when determining an environment  I came up with the following one-liner   string ActiveEnvironment   localEnv Contains  LIVE      LIVE     localEnv Contains  TEST      TEST     localEnv Contains  LOCAL      LOCAL    null      That way  if it can t find anything in the provided string that matches the  switch  conditions  it gives up and returns null  This could easily be amended to return a different value   It s not strictly a switch  more a cascading if statement but it s neat and it worked

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string message    This is test1   string   switchStrings      TEST1    TEST2     switch  switchStrings FirstOrDefault lt string gt  s   gt  message ToUpper   Contains s          case  TEST1             Do work         break      case  TEST2             Do work         break      default            Do work         break

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This will work in C  8 using a switch expresion var message    quot Some test message quot    message   message switch       string a when a Contains  quot test quot     gt   quot yes quot       string b when b Contains  quot test2 quot     gt   quot yes for test2 quot           gt   quot nothing to say quot      For further references https   docs microsoft com en-us dotnet csharp language-reference operators switch-expression

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Stegmenn nalied it for me but I had one change for when you have an IEnumerbale instead of a string   message like in his example    private static string GetRoles IEnumerable lt External Role gt  roles                    string   switchStrings      Staff    Board Member                 switch  switchStrings FirstOrDefault lt string gt  s   gt  roles Select t   gt  t RoleName  Contains s                                  case                      Staff                       roleNameValues     Staff                        break                  case                      Board Member                       roleNameValues     Director                        break                  default                      break

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Correct final syntax for  Mr  C s answer   With the release of VS2017RC and its C 7 support it works this way   switch message        case string a when a Contains  test2    return  no       case string b when b Contains  test    return  yes       You should take care of the case ordering as the first match will be picked  That s why  test2  is placed prior to test

User · Answer

Nope  switch statement requires compile time constants  The statement message Contains  test   can evaluate true or false depending on the message so it is not a constant thus cannot be used as a  case  for switch statement

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You can do the check at first and then use the switch as you like   For example   string str    parameter      test1  test2  test3      if   message Contains str   return     Then  switch str      case  test1       break    case  test2       break    default      break

[c#] Use string.Contains() with switch()

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