Why the GetType of DateTime is not a constant value

Question

I'm working on a switch statement with Type checking. The following code is working perfectly well for all the types, but, the challenge is with Nullable types.

  switch (Type.GetTypeCode( propertyInfos.PropertyType))
                    {
                        // Type code doesn't have reference with int, long, etc.,
                        case TypeCode.DateTime:
                            // Do the work for DateTime
                            break;
                        case TypeCode.Int32 :
                            // Do the work for Int32
                            break;
                        case TypeCode.Int64:
                            // Do the work for long
                            break;
                        case TypeCode.DateTime? :
                            break;
                        default:
                            break;
                    }

I have tried that to change as GetType and DateTime.Today.GetType().ToString() would give us System.DateTime as a string. But, when used the compiler throws error as that is not a valid Constant string. At any given time instance, DateTime.Today.GetType() would always gives us System.DateTime, why this is not accepted by compiler?

You have DateTime twice. The first case and the last non-default case are both DateTime. The message is "The switch statement contains multiple cases with the label value '16'". Voting to close. — ProgrammingLlama, Nov 29 '17 at 04:46

score 2 · Answer 1 · answered Nov 29 '17 at 05:09

I found this clever solution using a dictionary instead of a switch. Using that method, this should work for you:

public class Test {
    public DateTime A { get; set; }
    public Int32 B { get; set; }
    public Int64 C { get; set; }
    public DateTime? D { get; set; }
}

...Main...
        var @switch = new Dictionary<Type, Action> {
            { typeof(DateTime), () => Console.WriteLine("DateTime") },
            { typeof(Int32), () => Console.WriteLine("Int32") },
            { typeof(Int64), () => Console.WriteLine("Int64") },
            { typeof(DateTime?), () => Console.WriteLine("DateTime?") },
        };

        foreach (var prop in typeof(Test).GetProperties()) {
            @switch[prop.PropertyType]();
        }

score 0 · Accepted Answer · answered Nov 29 '17 at 05:00

I have used Nullable.GetUnderlyingType Method. I have applied type checking for nullable type then identified the nullable type and then finally specified the nullable's generic type.

if (Nullable.GetUnderlyingType(propertyType) != null)
            {
                // It's nullable
                Console.WriteLine(propertyType.GetGenericArguments()[0]);

            }

Why the GetType of DateTime is not a constant value

2 Answers2