ValueObjectGenerator NullReferenceException on VS 2022 17.6.4

[ebarkalov]

ValueObjectGenerator NullReferenceException on VS 2022 17.6.4

[Timovzl]

There’s an edge case I hadn’t considered. 😄

Great find. I’ll look into this in the next few days. I expect it will be easy to release a new patch version for this.

For now, may I recommend that you take IEnumerable as a parameter and use IReadOnlyList as the property? Assignment can go like this:

this.Values = values?.ToList() ?? throw new ArgumentNullException(nameof(values));

As a matter of fact, this will get you a true value object: one that is immutable. The defensive copy also helps ensure that we are not holding a list that the caller could modify after-the-fact.

(For single-valued objects, WrapperValueObject<T> can also make life easier.)

[Timovzl]

Hi @ebarkalov,

Thanks for your bug report!

If you create a blank solution, add the package, and paste in your ValueObject (working around any compiler errors), do you get the same error from the source generator?

Once we can reproduce it in such a minimal way, could you share the ValueObject so that I can investigate the bug?

[ebarkalov]

Hi @Timovzl

Thank you so much for your prompt reply!

Indeed, it does work on the blank solution!

Tried to clean my VS solution - no luck. Will continue investigation - will let you know if I find the cause.

[Timovzl]

Pity! I was hoping for an easy repro.

In that case, it will probably be quicker if you debug from within your own solution. You can do this as follows:

• Download this package's source.
• In your own project, remove the package reference to DomainModeling.
• Add both the DomainModeling and the DomainModeling.Generator projects to your solution.
• In your own project, add a project reference to DomainModeling.
• In your own project, add an analyzer project reference to DomainModeling.Generator. (You can just modify a regular project reference to match the linked example.)
• Uncomment this line in your local copy.
• Rebuild.

When you build with the Debugger.Launch() line enabled, VS will prompt you for which window to debug in. Hopefully this will reveal the exact line number where the null ref occurs. If not, you can even add a breakpoint to ValueObjectGenerator.TransformSyntaxNode to identify the problematic line manually.

Please share any findings, and let's see if we can nip this in the bud.

[ebarkalov]

Hi @Timovzl

I actually found the cause! It seems that ValueObjectGenerator does not like arrays. The following value object makes generator to fail.

[SourceGenerated]
public sealed partial class Color : ValueObject
{
  public Color(ushort[] rgb)
  {
    RGB = rgb;
  }

  public ushort[] RGB { get; }
}

[ebarkalov]

tuple.Type.ContainingNamespace is null.

[ebarkalov]

Thank you so much! Completely agree. Will do as you suggested!

[Timovzl]

Edit: The issue seems to be resolved when I change the problematic line to the following:

dataMemberHashCode = (tuple.Type.ContainingNamespace?.ToString() ?? "").GetStableHashCode64(dataMemberHashCode);

[Timovzl]

@ebarkalov A 2.0.1 prerelease package has been published.

Would you test the fix, please? Perhaps you could confirm that it works well with both your new and your old code - especially the arrays, of course.

[ebarkalov]

Hi @Timovzl

Thank you for the quick fix. I do confirm that arrays are working now in ValueObjects. Had to restart VS after upgrading package to pre-release for error to disappear.

As you mentioned in your comment before, it's better not to use arrays in value objects to support immutability principle. Switched to IReadOnlyList.

Thank you for all the support and such a great library that increases productivity when coding domain objects.