Detect MaxValue of generic parameter

Question

I want to write generic class which should work with byte and ushort types. What constraint should I use for this class? How can I detect MaxValue property inside of this class?

class MyClass<T>   // where T: ???
{
    void Foo()
    {
        int maxValue = T.MaxValue;    // how can I do this?
    }
}

If class was created with unexpected type, which doesn't contain MaxValue property, I don't care - for example, I can throw exception at runtime.

Answer 1

One way would be to leverage the new dynamic keyword:

void Main()
{
    Test(10);
    Test(10.234);
    Test((Byte)42);
    Test(true);
}

public void Test<T>(T value)
    where T : struct
{
    T maxValue = MaxValue((dynamic)value);
    maxValue.Dump();
}

public int MaxValue(int dummy)
{
    return int.MaxValue;
}

public double MaxValue(double dummy)
{
    return double.MaxValue;
}

public byte MaxValue(byte dummy)
{
    return byte.MaxValue;
}

public object MaxValue(object dummy)
{
    // This method will catch all types that has no specific method
    throw new NotSupportedException(dummy.GetType().Name);
}

Or, you could use reflection to obtain the MaxValue field:

void Main()
{
    Test(10);
    Test(10.234);
    Test((Byte)42);
    Test(true);
}

public void Test<T>(T value)
    where T : struct
{
    FieldInfo maxValueField = typeof(T).GetField("MaxValue", BindingFlags.Public
        | BindingFlags.Static);
    if (maxValueField == null)
        throw new NotSupportedException(typeof(T).Name);
    T maxValue = (T)maxValueField.GetValue(null);
    maxValue.Dump();
}

You can test these two programs through LINQPad.

Answer 2

Try something like this

    public T GetMaxValue()
    {
        object maxValue = default(T);
        TypeCode typeCode = Type.GetTypeCode(typeof(T));
        switch (typeCode)
        {
            case TypeCode.Byte:
                maxValue = byte.MaxValue;
                break;
            case TypeCode.Char:
                maxValue = char.MaxValue;
                break;
            case TypeCode.DateTime:
                maxValue = DateTime.MaxValue;
                break;
            case TypeCode.Decimal:
                maxValue = decimal.MaxValue;
                break;
            case TypeCode.Double:
                maxValue = decimal.MaxValue;
                break;
            case TypeCode.Int16:
                maxValue = short.MaxValue;
                break;
            case TypeCode.Int32:
                maxValue = int.MaxValue;
                break;
            case TypeCode.Int64:
                maxValue = long.MaxValue;
                break;
            case TypeCode.SByte:
                maxValue = sbyte.MaxValue;
                break;
            case TypeCode.Single:
                maxValue = float.MaxValue;
                break;
            case TypeCode.UInt16:
                maxValue = ushort.MaxValue;
                break;
            case TypeCode.UInt32:
                maxValue = uint.MaxValue;
                break;
            case TypeCode.UInt64:
                maxValue = ulong.MaxValue;
                break;
            default:
                maxValue = default(T);//set default value
                break;
        }

        return (T)maxValue;                             
    }

Answer 3

You can only use struct as a constraint which will only allow value types for T. Every specific value type as a constraint will be rejected by the compiler. So you have to do a runtime check whether T is one of your allowed types.

The only way to get the MaxValue of your (unknown) type T is reflection with something like this:

typeof(T).GetField("MaxValue").GetValue(null);