Bug on handling conversion from a choice type

[baseTwo]

Also follow discussion on cql choice types #604

The following cql results in the following c#:

define "Initial Population":
  (AgeInYearsAt(start of "Measurement Period") >= 16) and exists("Injury due to falling rock within measurement period")

	private IEnumerable<Condition> Injury_due_to_falling_rock_within_measurement_period_Value()
	{
		CqlValueSet a_ = this.Injury_due_to_falling_rock();
		IEnumerable<Condition> b_ = context.Operators.RetrieveByValueSet<Condition>(a_, default);
		bool? c_(Condition C)
		{
			DataType e_ = C?.Onset;
			object f_ = context.Operators.LateBoundProperty<object>(e_, "value"); // REF#1
			CqlInterval<CqlDateTime> g_ = this.Measurement_Period();
			bool? h_ = context.Operators.In<CqlDateTime>(f_ as CqlDateTime /* REF#2 */, g_, default);

			return h_;
		};
		IEnumerable<Condition> d_ = context.Operators.Where<Condition>(b_, c_);
		return d_;
	}

The latebound property returns a choice type (REF#1). At this stage we do not have a C# equivalent type for this, so object is used. Unfortunately this can easily allow one to make assumptions when casting, such as at REF#2, where a safe cast is made to CqlDateTime. At runtime, the actual type was a string, so this did not work.

Instead, when choice types are to be converted, the runtime ICqlOperators.Convert<T>(object) must be invoked.

[EvanMachusak]

The CQL in the issue doesn't match the generated C#. What is the CQL for "Injury due to falling rock within measurement period"?

I don't believe the proposed fix is correct.

Specifically:

At runtime, the actual type was a string, so this did not work.

Things are allowed to not work if the runtime type is not correct. I do not think invoking any kind of conversion is correct in this case.

My memory is hazy but I do notice that value is the property being accessed. There is a lot of weirdness with value property accessors on FHIR types that created issues like these in the past. I think we had some code in 1.0 to ignore accesses to value properties in some cases because it causes type confusion.

In the Firely model, what does Condition.Onset.value return? Is it a string? What is Condition.Onset? Is it a FHIR dateTime? Why isn't FHIRHelpers.ToDateTime being invoked so that In can be called?

There are a lot of questions here.

[alexzautke]

RR23_LIB_Umbrella_Measure.json

Here’s the library that we used for testing