An attribute argument must be a constant expression, ...- Create an attribute of type array

Solution 1:

This supplements the information Simon already gave.

I found some documentation here: Attribute parameter types:

The types of positional and named parameters for an attribute class are limited to the attribute parameter types, which are:

• One of the following types: bool, byte, char, double, float, int, long, sbyte, short, string, uint, ulong, ushort.
• The type object.
• The type System.Type.
• An enum type, provided it has public accessibility and the types in which it is nested (if any) also have public accessibility (Attribute specification).
• Single-dimensional arrays of the above types. (emphasis added by me)

A constructor argument or public field which does not have one of these types, cannot be used as a positional or named parameter in an attribute specification.

The last bullet point explains your syntax error. You've defined a one-dimensional array, but it should only be of primitive types, string, etc. as listed in the previous bullet points.

Solution 2:

Attribute arguments must be compile-time constant. That means that the compiler must be able to "bake in" the values of the arguments when the assembly is compiled. new ReferenceType() is not constant - it must be evaluated at runtime to determine what it is.

Interestingly, this is a little bit flimsy in that there are some edge cases to that rule. Other than those though, you cannot do what you're trying to do.