C switch on type

Question

Possible Duplicate    C  - Is there a better alternative than this to   39 switch on type  39         C  doesn t support switching on the type of an object  What is the best pattern of simulating this   switch  typeof MyObj       case Type1      case Type2      case Type3

User · Answer

There is a simple answer to this question which uses a dictionary of types to look up a lambda function. Here is how it might be used:

var ts = new TypeSwitch()
    .Case((int x) => Console.WriteLine("int"))
    .Case((bool x) => Console.WriteLine("bool"))
    .Case((string x) => Console.WriteLine("string"));

ts.Switch(42);
ts.Switch(false);
ts.Switch("hello");

There is also a generalized solution to this problem in terms of pattern matching (both types and run-time checked conditions):

var getRentPrice = new PatternMatcher<int>()
    .Case<MotorCycle>(bike => 100 + bike.Cylinders * 10) 
    .Case<Bicycle>(30) 
    .Case<Car>(car => car.EngineType == EngineType.Diesel, car => 220 + car.Doors * 20)
    .Case<Car>(car => car.EngineType == EngineType.Gasoline, car => 200 + car.Doors * 20)
    .Default(0);

var vehicles = new object[] {
    new Car { EngineType = EngineType.Diesel, Doors = 2 },
    new Car { EngineType = EngineType.Diesel, Doors = 4 },
    new Car { EngineType = EngineType.Gasoline, Doors = 3 },
    new Car { EngineType = EngineType.Gasoline, Doors = 5 },
    new Bicycle(),
    new MotorCycle { Cylinders = 2 },
    new MotorCycle { Cylinders = 3 },
};

foreach (var v in vehicles)
{
    Console.WriteLine("Vehicle of type {0} costs {1} to rent", v.GetType(), getRentPrice.Match(v));
}

User · Answer

See gjvdkamp s answer below  this feature now exists in C   I usually use a dictionary of types and delegates  var  switch   new Dictionary lt Type  Action gt          typeof Type1        gt               typeof Type2        gt               typeof Type3        gt              switch typeof MyType       It s a little less flexible as you can t fall through cases  continue etc  But I rarely do so anyway

User · Answer

I have used this form of switch-case on rare occasion  Even then I have found another way to do what I wanted  If you find that this is the only way to accomplish what you need  I would recommend  Mark H s solution     If this is intended to be a sort of factory creation decision process  there are better ways to do it  Otherwise  I really can t see why you want to use the switch on a type     Here is a little example expanding on Mark s solution  I think it is a great way to work with types     Dictionary lt Type  Action gt  typeTests   public ClassCtor         typeTests   new Dictionary lt Type  Action gt           typeTests typeof int          gt  DoIntegerStuff        typeTests typeof string          gt  DoStringStuff        typeTests typeof bool          gt  DoBooleanStuff       private void DoBooleanStuff          do stuff    private void DoStringStuff           do stuff    private void DoIntegerStuff           do stuff    public Action CheckTypeAction Type TypeToTest        if  typeTests Keys Contains TypeToTest           return typeTests TypeToTest        return null     or some other Action delegate

User · Answer

Update  This got fixed in C  7 0 with pattern matching  switch  MyObj      case Type1 t1       case Type2 t2      case Type3 t3    Old answer   It is a hole in C  s game  no silver bullet yet   You should google on the  visitor pattern  but it might be a little heavy for you but still something you should know about   Here s another take on the matter using Linq  http   community bartdesmet net blogs bart archive 2008 03 30 a-functional-c-type-switch aspx  Otherwise something along these lines could help      nasty   switch MyObj GetType ToString       case  Type1   etc       clumsy    if myObj  is Type1 then if myObj is Type2 then   etc

User · Answer

I did it one time with a workaround  hope it helps   string fullName   typeof MyObj  FullName   switch  fullName        case  fullName1       case  fullName2       case  fullName3

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