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FHIR / sushi

SUSHI (aka "SUSHI Unshortens Short Hand Inputs") is a reference implementation command-line interpreter/compiler for FHIR Shorthand (FSH).
Apache License 2.0
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Cannot assign aliased instances #713

Open ngfreiter opened 3 years ago

ngfreiter commented 3 years ago

The following works fine:

Profile: MyOb
Parent: Observation
* ^contained[0] = http://hl7.org/fhir/StructureDefinition/Patient

but this does not work:

Alias: bar = http://hl7.org/fhir/StructureDefinition/Patient

Profile: MyOb
Parent: Observation
* ^contained[0] = bar

I think we would expect that these two cases should work the same.

ngfreiter commented 3 years ago

Then again maybe we wouldn't expect these two cases to be the same. We have already a precedent of an alias being used to represent a string value in an assignment rule. I'm not sure how we decide whether an alias should represent a string or an inline instance.

cmoesel commented 3 years ago

Isn't that determination made by the type it is assigned to? I.e., if it is a string-like type, assign as a string, otherwise treat as an instance. We do something kind of like that w/ concepts because foo#bar can be a code, Coding, CodeableConcept, or Quantity units depending on what it is being assigned to.

ngfreiter commented 3 years ago

Yeah I think that could work. But I do think that fixing this bug may then require some significant refactoring, since currently we decide if something is an instance or not in import. If we are making that decision based on the type being assigned to, we may need to change that.

cmoesel commented 3 years ago

Ah. I forgot that bit. So, the string use... we did that in order to support things like:

* compose.include[0].system = LNC

right? Just trying to remember the different use cases...

ngfreiter commented 3 years ago

Well when an instance is assigned, its value is still just a string, but with the isInstance flag set. Before the ability to assign instances, aliases would always resolve to a string, and on the import side it would be impossible to tell if those strings refer to an instance or not, so the isInstance flag would not get set.