.NET Standard assembly attribute with DateTime parameter

Question

Background

I'm trying to implement a custom attribute that can be applied to a .NET assembly to indicate an expiry date (the date after which the developers do not support the use of a pre-release version that has been distributed for testing). It has to be written in .NET Standard (2.0).

I know that I can't pass a DateTime in as a parameter so I'm passing in a string that conforms to ISO8601 (YYYY-MM-DD) and then using DateTime.Parse() to convert to a DateTime.

The attribute I've got so far is below:

[AttributeUsage(AttributeTargets.Assembly, Inherited = false, AllowMultiple = false)]
public sealed class UnstableReleaseExpiryAttribute : Attribute
{
    public UnstableReleaseExpiryAttribute(string expiryDate)
    {
        ExpiryDate = expiryDate;
    }
    public DateTime Expiry
    {
        get
        {
            if (ExpiryDate != null && DateTime.TryParse(ExpiryDate, out DateTime expiry))
                return expiry;

            return DateTime.MaxValue;
        }
    }
    public string ExpiryDate { get; }
}

This is how I intend to use it:

[assembly: UnstableReleaseExpiry("2018-05-24")]

Question

Is there a way to validate the string input using, say, a regex expression, and stop it from being compiled if the date isn't actually parsable? I looked around and thought that inheriting from ValidationAttribute would be the way to do it, but it doesn't appear to be available in .NET Standard 2.0. Are there any other ways of doing this?

score 2 · Accepted Answer · answered May 24 '18 at 08:05

No. There isn't at this point of time. ValidationAttribute is only an "annotation" about what should be the format of a field/property. Other C# code must activate it.

You could create a code analysis rule to check for this.
Similar questions: Is it possible to query custom Attributes in C# during compile time ( not run-time ), Postsharp compile-time validation on interface methods . You could use Fody instead of PostSharp probably
Simple solution I have used (because handling post-compilation steps is a pain, and code analyzers can be disabled): if you have a unit test project, make a test that uses reflection to find all the usage of the attribute and checks it.

.NET Standard assembly attribute with DateTime parameter

Background

Question

1 Answers1