P4074

Code

P4074

Message

THIS^ outside a function block or SUPER^ without a base type

This error occurs when THIS^ is used outside a function block, or SUPER^ is used in a function block that has no base type.

THIS^ names the function block instance that the code is running on, so it only has a meaning inside a function block: in its body, its methods and its property accessors. A program or a function has no such instance. SUPER^ names the same instance seen as its base type, so it also needs a function block that EXTENDS another.

Example

The following code will generate error P4074:

FUNCTION_BLOCK FB_Motor
    VAR
        speed : INT;
    END_VAR
    METHOD Stop
        SUPER^.Stop();  (* Error: FB_Motor has no base type *)
    END_METHOD
END_FUNCTION_BLOCK

FB_Motor does not extend another function block, so there is no base implementation for SUPER^ to call.

To fix this error, call the function block’s own member with THIS^, or derive the function block from the base type that declares the member:

FUNCTION_BLOCK FB_Motor
    VAR
        speed : INT;
    END_VAR
    METHOD Stop
        THIS^.speed := 0;
    END_METHOD
END_FUNCTION_BLOCK

See Also

• THIS and SUPER — THIS and SUPER

• EXTENDS — EXTENDS

Think IronPLC is wrong about this?

If you believe this diagnostic is incorrect, open an issue on GitHub with a small sample that demonstrates the problem.