Question

I’m trying to compile a project containing this method;

public void Send<T>(object o) where T : struct {
    BinaryWriter bw = new BinaryWriter(stream);
    bw.Write((T)o);
}

I inspired from this method (working);

public static T Cast<T>(object o) {
    return (T)o;
}

BinaryWriter.Write function supports primitive types for parameters, so I thought I could use it like that. However, Visual Studio says “The best overloaded method match for ‘System.IO.BinaryWriter.Write(bool)’ has some invalid arguments“

I’m trying to avoid writing a long switch statement containing every primitive type and add a parameter to method for choosing the type. This is ugly and doesn’t seem right.

This is simple and elegant:

• Send< int>(123);
• Send< bool>(true);

But why isn’t it working? And what is the right way to do it?

Answer 1

Overload resolution is performed at compile time. So the compiler’s trying to find a method with a parameter which will be valid *whatever type T is, (within its constraints, which don’t help here). It can’t find such a method. Given that the only constraint is that T must be a struct, the only non-generic parameter type that would be valid would be object (via boxing).

If your aim was to use whichever overload was appropriate based on the execution-time type of the object, you’ll need to either use dynamic typing, like this:

public void Send(dynamic d) {
    BinaryWriter bw = new BinaryWriter(stream);
    bw.Write(d);
}

… or fetch and execute the right overload with reflection (which is sort of what dynamic typing would do).