SA0044: Declarations with reference to interface

Detects declarations with REFERENCE TO interfaces and declarations of VAR_IN_OUT variables with interfaces (implicitly implemented by means of REFERENCE TO)

Justification: 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 result in unwanted behavior.

Importance: High

FUNCTION_BLOCK POU
VAR_INPUT
    inst_itf2 : ITF;
END_VAR
VAR_OUTPUT
    inst_itf3 : ITF;
END_VAR
VAR_IN_OUT
    inst_itf4 : ITF;                // SA0044
END_VAR

PROGRAM PLC_PRG
VAR
    inst : POU;
    itf_inst1 : ITF;
    itf_ref : REFERENCE TO ITF; // SA0044
END_VAR