Question

Is it possible to combine a normal class with a partial class like this:

public class ClassA
{
    public string PropertyA {get; set;}
}

public partial class ClassA
{
    public string PropertyB {get; set;}
}

The result of the code should look:

var instance = new ClassA();

instance.PropertyA = "Something";
instance.PropertyB = "Something else";

Does C# support this pattern?

Thank you all in advance!

Answer 1

No. All parts of a partial class have to include the partial modifier. From section 10.2 of the C# 4 language specification:

Each part of a partial type declaration must include a partial modifier. It must have the same name and be declared in the same namespace or type declaration as the other parts. The partial modifier indicates that additional parts of the type declaration may exist elsewhere, but the existence of such additional parts is not a requirement; it is valid for a type with a single declaration to include the partial modifier.

All parts of a partial type must be compiled together such that the parts can be merged at compile-time into a single type declaration. Partial types specifically do not allow already compiled types to be extended.

(Emphasis mine.)