C# generics: cast generic type to value type

Question

I have a generic class which saves value for the specified type T. The value can be an int, uint, double or float. Now I want to get the bytes of the value to encode it into an specific protocol. Therefore I want to use the method BitConverter.GetBytes() but unfortunately Bitconverter does not support generic types or undefined objects. That is why I want to cast the value and call the specific overload of GetBytes(). My Question: How can I cast a generic value to int, double or float? This doesn't work:

public class GenericClass<T>
    where T : struct
{
    T _value;

    public void SetValue(T value)
    {
        this._value = value;
    }

    public byte[] GetBytes()
    {
        //int x = (int)this._value;
        if(typeof(T) == typeof(int))
        {
            return BitConverter.GetBytes((int)this._value);
        }
        else if (typeof(T) == typeof(double))
        {
            return BitConverter.GetBytes((double)this._value);
        }
        else if (typeof(T) == typeof(float))
        {
            return BitConverter.GetBytes((float)this._value);
        }
    }
}

Is there a possibility to cast an generic value? Or is there another way to get the bytes?

Answer 1

First off, this is a really bad code smell. Any time you're doing a type test on a type parameter like this odds are good you're abusing generics.

The C# compiler knows that you are abusing generics in this way and disallows the cast from the value of type T to int, etc. You can turn off the compiler getting in your way by casting the value to object before you cast it to int:

return BitConverter.GetBytes((int)(object)this._value);

Yuck. Again, it would be better to find another way to do this. For example:

public class NumericValue
{
    double value;
    enum SerializationType { Int, UInt, Double, Float };
    SerializationType serializationType;        

    public void SetValue(int value)
    {
        this.value = value;
        this.serializationType = SerializationType.Int
    }
    ... etc ...

    public byte[] GetBytes()
    {
        switch(this.serializationType)
        {
            case SerializationType.Int:
                return BitConverter.GetBytes((int)this.value);
            ... etc ...

No generics necessary. Reserve generics for situations that are actually generic. If you've written the code four times one for each kind of type, you haven't gained anything with generics.