C# use where keyword on classes with XmlElementAttribute properties

Question

This is what I'm looking to do:

public class NormalClass
{
    [XmlAttribute]
    public int Example;
}

[XmlRoot]
public class GenericClass<T> where T : HasXmlElementAttribute
{
    [XmlArray]
    public List<T> Variables;
}

I thought where T : IXmlSerializable might work, but it did not.

Is this even possible to do? If so, what is the proper way?

Additional Thoughts/Edit

Is there a way to achieve this same goal? Is there a way to only allow classes that can be xml serialized?

Thanks

Answer 1

No, you cannot use generic type constraints to limit the type parameters by what attributes they are decorated with. You can only use generic type constraints to limit type parameters by:

• What base the type parameter inherits
• What interfaces the type parameter implements
• What constructors the type parameter provides
• Whether the type parameter is a value type or a reference type

Further Reading:

• Constraints on Type Parameters (C# Programming Guide)

Answer 2

Attributes are not part of the type system.

You cannot constrain a type parameter based on the presence of an attribute.

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Side note: This justification is not quite valid; constructors aren't part of the type system either, yet : new() is a valid constraint.