Metalama Community•2y ago

How do I invoke (and cast) an introduced generically typed field?

Bear with me - there's a lot going on here. Also Discord is funky about styling my code, so I'm handwriting it (pardon any typos). At a high level, let me explain where I'm trying to go and then I'll get into the issue. I want to attach an attribute to a target type that defines a type (TEntity) and another type (TEntityId) so I can use these to introduce some advice later on. I can retrieve those no problem - each is saved as an INamedType on the BuildAspect method. I then want to iterate through most of the properties of the TEntity type itself and introduce at least one field for several of them, but the type of the field depends on the type of the property itself. Again, this is set up and works fine. I save all the references to the introductions in a dictionary keyed by a reproducible mechanism to link the properties with the introduced types. Again, this works fine. My target type implements a base type which has a bunch of event callbacks in place. What I want to do is replace the last methods in those event callback chains with a method that can do operations against some or all of these introduced fields and this is where I'm having some difficulty. I can pass along the produced IIntroductionAdviceResult<IField> via tags, but my problem is that I can't figure out how to assign the appropriate type to it. Now, typically I'd do something like this:

[Template]
private void DoSomething<[CompileTime]TMyType>(IMethod myMethod)
{
  var thisIsMyMethod = (TMyType) myMethod.Invoke()
  //Use it as though it's cast as a TMyType now
  //...
}

[Template]
private void DoSomething<[CompileTime]TMyType>(IMethod myMethod)
{
  var thisIsMyMethod = (TMyType) myMethod.Invoke()
  //Use it as though it's cast as a TMyType now
  //...
}

But the issue here is that the type is only known by the field itself and only as part of this compilation pipeline. As a result, I cannot do the following (or can I?):

[Template]
internal void RebuildNotificationAsyncCallback(
  IIntroductionAdviceResult<IFIeld> adviceField
)
{
  //I can get the type of the field off the type declaration itself...
  var fieldType = adviceField.Declaration.Type; //...but then I cannot then use this with an 'as' or 'is' nor can I cast with a (fieldType)whatever.Value;
  //So when I then get my value for it, it's stuck cast as a `dynamic?` and it's unclear how to proceed
  var myField = adviceField.Declaration.Value; //Type = dynamic?
}

[Template]
internal void RebuildNotificationAsyncCallback(
  IIntroductionAdviceResult<IFIeld> adviceField
)
{
  //I can get the type of the field off the type declaration itself...
  var fieldType = adviceField.Declaration.Type; //...but then I cannot then use this with an 'as' or 'is' nor can I cast with a (fieldType)whatever.Value;
  //So when I then get my value for it, it's stuck cast as a `dynamic?` and it's unclear how to proceed
  var myField = adviceField.Declaration.Value; //Type = dynamic?
}

I could try using meta since this is a template, but it's a similar problem - the only thing that knows what type it is is the method advice itself and I can't cast with that. Is there a helper method I'm missing somewhere to allow invocation of arbitrary typed introduced fields? Or how else might I go about using the adviceField in this template? Thank you!

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How do I invoke (and cast) an introduced generically typed field?