Metalama Community•2y ago

Override property with BuildAspect

I create exceptions inheriting from Exception and putting the [BusinessException] attribute. I want to override the Message property using string.Format with the primary constructor parameters. For example, the next class:

[BusinessException]
public class UserAlreadyExistsException(int age, string email) : Exception;

[BusinessException]
public class UserAlreadyExistsException(int age, string email) : Exception;

I started with [Introduce], but later I noticed I need BuildAspect to access constructors. I've tried with this, but I don't know how to do complete the code. The goal is to have: string.Format("The user with age {0} and email {1} already exists", age, email); Code: https://try.metalama.net/#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-CWOCAxYcCTEK9widT7VZ6vypiDg8iI9qBkX6wmAEiioQdJLLWe5-pwlIMDB7gAZ+8o5t+Kanl2MhWCc-yFrM8xWIsbBDucYRLCh6EYRWsg4XhTyuq8Sz1hujboMOoSGpRqK2rCtosuQICSIgHAgCyHwskAA

5 Replies

Petr Onderka•2y ago

You can access constructors from a template, like this:

[Introduce(WhenExists = OverrideStrategy.Override)]
public string Message
{
    get
    {
        var parameters = meta.Target.Type
            .Constructors
            .First()
            .Parameters;

        var template = "The user with age {0} and email {1} already exists";
        return string.Format(template, parameters[0].Value, parameters[1].Value);
    }
}

[Introduce(WhenExists = OverrideStrategy.Override)]
public string Message
{
    get
    {
        var parameters = meta.Target.Type
            .Constructors
            .First()
            .Parameters;

        var template = "The user with age {0} and email {1} already exists";
        return string.Format(template, parameters[0].Value, parameters[1].Value);
    }
}

But keep in mind that Metalama does not support preview features of C#, so this is not guaranteed to work. (And to make sure you're aware of this, we require you to specify <MetalamaAllowPreviewLanguageFeatures>true</MetalamaAllowPreviewLanguageFeatures> in your project file.) In particular, there are some things that don't work well: 1. It doesn't work if the exception class has no body (;), it requires at least an empty body ({}). 2. There is no way to tell if a constructor is primary.

AndreuOP•2y ago

Thanks! But can I do anything to use an empty body? For example, generate properties and use string.Format with them, use a preview version of Metalama, anything?

Petr Onderka•2y ago

Do you mean no body? (Empty body should work.) There is currently nothing you can do, Metalama simply does not expect that a class could have no body and so it won't work if you want to introduce something there.

AndreuOP•2y ago

Yes, I mean that. Then, if I can't apply any hack meanwhile it gets proper support, please, can you tell me what's the approximate time Metalama will need to support the new C# version? It's because my library needs yes or yes C# 12 and .NET 8

Petr Onderka•2y ago

Proper support will come very soon after Microsoft releases C# 12, which will be in November.

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Override property with BuildAspect