c# 7.0: switch on System.Type

Question

No existing question has an answer to this question.

In c# 7, can I switch directly on a System.Type?

When I try:

    switch (Type)         


        

Answer 1

@toddmo suggested the following:

switch (true)
{
    case bool _ when extruder.Temperature < 200:
        HeatUpExtruder();
        break;

    // etc..
    default:
        StartPrintJob();
        break;
}

...but why not go even further in his pursuit of simplicity. The following works just as well without needing the bool type qualification, nor the extraneous _ dummy variable:

switch (true)
{
    case true when extruder.Temperature < 200:
        HeatUpExtruder();
        break;

    // etc.
    default:
        StartPrintJob();
        break;
}

Answer 2

The (already linked) new pattern matching feature allows this.

Ordinarily, you'd switch on a value:

switch (this.value) {
  case int intValue:
    this.value = Math.Max(Math.Min(intValue, Maximum), Minimum);
    break;
  case decimal decimalValue:
    this.value = Math.Max(Math.Min(decimalValue, Maximum), Minimum);
    break;
}

But you can use it to switch on a type, if all you have is a type:

switch (type) {
  case Type intType when intType == typeof(int):
  case Type decimalType when decimalType == typeof(decimal):
    this.value = Math.Max(Math.Min(this.value, Maximum), Minimum);
    break;
}

Note that this is not what the feature is intended for, it becomes less readable than a traditional if...else if...else if...else chain, and the traditional chain is what it compiles to anyway. I do not recommend using pattern matching like this.

Answer 3

I found a simple and efficient way. It requires C# V7 to run. The switch("") means all cases will be satisfied up to the when clause. It uses the when clause to look at the type.

List<Object> parameters = new List<object>(); // needed for new Action
parameters = new List<object>
{
    new Action(()=>parameters.Count.ToString()),
    (double) 3.14159,
    (int) 42,
    "M-String theory",
    new System.Text.StringBuilder("This is a stringBuilder"),
    null,
};
string parmStrings = string.Empty;
int index = -1;
foreach (object param in parameters)
{
    index++;
    Type type = param?.GetType() ?? typeof(ArgumentNullException);
    switch ("")
    {
        case string anyName when type == typeof(Action):
            parmStrings = $"{parmStrings} {(param as Action).ToString()} ";
            break;
        case string egStringBuilder when type == typeof(System.Text.StringBuilder):
            parmStrings = $"{parmStrings} {(param as System.Text.StringBuilder)},";
            break;
        case string egInt when type == typeof(int):
            parmStrings = $"{parmStrings} {param.ToString()},";
            break;
        case string egDouble when type == typeof(double):
            parmStrings = $"{parmStrings} {param.ToString()},";
            break;
        case string egString when type == typeof(string):
            parmStrings = $"{parmStrings} {param},";
            break;
        case string egNull when type == typeof(ArgumentNullException):
            parmStrings  = $"{parmStrings} parameter[{index}] is null";
            break;
        default: throw new System.InvalidOperationException();
    };
} 

This leaves parmStrings containing...

System.Action 3.14159, 42, M-String theory, This is a stringBuilder, parameter[5] is null