Special rule for protected connectors?

[eshmoylova]

I found this model in the Buildings library. In the protected section it has the following connector:

  Buildings.Fluid.FMI.Interfaces.FluidProperties bacPro_internal(
    redeclare final package Medium = Medium)...;

[FluidProperties](https://github.com/lbl-srg/modelica-buildings/blob/master/Buildings/Fluid/FMI/Interfaces/FluidProperties.mo) is a connector containing another connector:

  Buildings.Fluid.FMI.Interfaces.MassFractionConnector X_w...;

MassFractionConnector is in turn defined as:

connector MassFractionConnector =
  Modelica.Units.SI.MassFraction...;

This connector is then used as:

  connect(bacPro_internal.X_w, X_wZon_internal);

where X_wZon_internal is declared as an output (also protected):

  Modelica.Blocks.Interfaces.RealOutput X_wZon_internal(
    final unit="kg/kg")

So, we have non-causal connector connected to an output. MapleSim rejects this model (and any model containing it as component) for that reason. One of the models that uses it, for example, is Buildings.Fluid.FMI.Conversion.Validation.AirToOutlet. It is marked as a simulation model and has a Dymola script. So, I'm assuming it works in Dymola.

I wonder if that means that connector restrictions do not apply to protected connectors?

[HansOlsson]

Design meeting.

There seems to be two solutions:

• Update the library
• Change the rules to make an exception for some connectors:
  • If neither have causal parts nor flow we allow the connector class (for balancing), and require that we add input/output when using it
  • Additionally for protected connector component we allow it without input/output

[HansOlsson]

Seems that some tools (e.g., Dymola 2023) have such a special rule for protected connectors.