parameter 'T' has the same name as the type parameter [closed]

Question

I'm trying to write a method that accepts a generic input and returns null if the input is default and an XElement otherwise.

Btw, I'm pretty green at generic methods, and apparently at google-fu.

Here's what I have so far:

public static class ConversionClass<T>
{
    public static XElement newXElementOrNull<T>(string name, T val)
    {
        if ((T.type == "String") && (val == String.Empty))
        {
            return null;
        }

        if (val == default(T))
        {
            return null;
        }
        else
        {
            return new XElement(name, val);
        }
    }
}

For some reason, C# does not like this.

It balks on the method signature (newXElementOrNull) saying:

Type parameter 'T' has the same name as the type parameter from outer type 'AddXMLTest.Converter'

And it highlights the T in the angled brackets and the T in the parameter.

To make matters worse it doesn't like the val == default(T) part because it says Operator '==' cannot be applied to operands of type 'T' and 'T'.

What am I doing wrong?

Answer 1

Apparently this method is inside a class that already specifies <T>. That means that you can omit this type parameter, methods of a generic class are automatically generic too.

I would expect T.type to cause errors as well but it depends on the type-constraints on the outer class. To get a full answer, post the outer definition (not all members) of that class.

it doesn't like the val == default(T)

That is most likely a follow-up error of the first.

Answer 2

Type parameter 'T' has the same name as the type parameter from outer type 'AddXMLTest.Converter'

So the class outside of this method (not shown) must be using <T> as well. You won't be able to do that. Name it (on the method that is) something like <K>.

To make matters worse it doesn't like the val == default(T) part because it says Operator '==' cannot be applied to operands of type 'T' and 'T'.

This should be resolved when you stop using <T> and change it so something like default(K).

Further, I'm pretty sure that this T.type isn't going to compile. I'm pretty sure that evaluation should be something like:

if ((val is typeof(string) && string.IsNullOrEmpty(val))