.net - An attribute argument must be a constant expression

Question

Is there any workaround for the following issue?

An attribute argument must be a constant expression

I want to use decimals in an attribute’s parameter.

Answer 1

Unfortunately you can't use decimals in attribute values, as the CLR itself doesn't really know about System.Decimal type - it's not a primitive type like int, double etc. The C# compiler basically fakes it for const fields of type decimal, but it can't achieve the same effect with attributes.

From the C# 3 spec, section 17.1.3:

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 (§17.2).
• Single-dimensional arrays of the above types.

Then later in section 17.2:

An expression E is an attribute-argument-expression if all of the following statements are > true:

• The type of E is an attribute parameter type (§17.1.3).
• At compile-time, the value of E can be resolved to one of the following:
  • A constant value.
  • A System.Type object.
  • A one-dimensional array of attribute-argument-expressions.