CLS compliant attributes and array parameters

Question

I have created an attribute that accepts a (params) array in its constructor.

internal class MyTestAttribute : Attribute
{
    public MyTestAttribute (params Options[] options)
    {
        ....
    }
}

Option here is an enum (with lots of values), so a sample call site will be

[MyTest(Option.One, Option.Three)]
internal void SomeMethod(int param1, long param2)
{
  ....
}

Everything is peachy so far, and the setup works, but I'm receiving an "Arrays as attribute arguments is not CLS-compliant" warning on each call-site. Now, I have to admit that I do not need to use this assembly from anywhere other that C#, nor do I do warnings-as-errors, but the hundreds of warnings are getting annoying.

The obvious solution is to turn off CLS-compliance, but at the moment I can't do that.

Is there some other approach to the creation of the attribute that will still do the same thing, but get rid of the warnings?

Bendy

Answer 1

Two options:

1: you could add some overloads instead:

private MyTestAttribute(Option[] options) {...}
public MyTestAttribute(Option option0)
          : this(new[] {option0}) {}
public MyTestAttribute(Option option0, Option option1)
          : this(new[] {option0, option1}) {}
public MyTestAttribute(Option option0, Option option1, Option option2)
          : this(new[] {option0, option1, option2}) {}
// add a few more, without going crazy

2: if Options is an enum, mark the enum as a [Flags] enum, and have the caller combine them:

[MyTest(Option.One | Option.Two)]

with:

[Flags]
public enum Option {
     None = 0,
     One = 1,
     Two = 2,
     Three = 4,
     Four = 8,
     ...
}

Clarkclarke

Arg, beat me! But why is CLS complaining on an internal attribute class? – Cocaine

Yes, Option is an enum, and the call site will use at most three or four options, so this is a great solution. Tnx, I had a feeling I was overlooking something obvious :) – Bendy

@leppie, it's not complaining on the definition of the attribute (it does if it's public), it's complaining on the public call sites. – Bendy

Answer 2

"Arrays as attribute arguments is not CLS-compliant"

Exactly what it says.

The only workaround is to create explicit parameters, eg:

internal class MyTestAttribute : Attribute
{
    public MyTestAttribute(Option o1) : this(new Option[] { o1 }) {}
    public MyTestAttribute(Option o1, Option o2) : 
      this(new Option[] { o1, o2 }) {}

    MyTestAttribute (Options[] options)
    {
        ....
    }
}

Note: It is funny though that CLS is being complianed about given the attribute class is internal. AFAIK, CLS is only meant to be validated on possible external members (public/protected).

Cocaine

It's not complaining on the definition of the attribute (it does if it's public), it's complaining on the public call sites. – Bendy