SA0044: Declarations with reference to interface

Function	Determines declarations with REFERENCE TO <interface> and declarations of VAR_IN_OUT variables with the type of an interface (realized implicitly via REFERENCE TO).
Reason	An interface type is always implicitly a reference to an instance of a function block that implements this interface. A reference to an interface is therefore a reference to a reference and can lead to unwanted behavior.
Importance	High

Samples:

I_Sample is an interface defined in the project.

Function block FB_Sample:

FUNCTION_BLOCK FB_Sample
VAR_INPUT
    iInput      : I_Sample; 
END_VAR
VAR_OUTPUT
    iOutput     : I_Sample; 
END_VAR
VAR_IN_OUT
    iInOut1     : I_Sample;              // => SA0044

    {attribute 'analysis' := '-44'}
    iInOut2     : I_Sample;              // no error SA0044 because rule is deactivated via attribute
END_VAR

MAIN program:

PROGRAM MAIN 
VAR
    fbSample    : FB_Sample;
    iSample     : I_Sample; 
    refItf      : REFERENCE TO I_Sample; // => SA0044
END_VAR