Object Oriented Programming

IEC 61131-3 Edition 3 (2013) added object-oriented programming to the standard. A function block type can declare methods, it can be derived from another by extension, one or more interfaces can describe a shared set of method signatures, and a type can be declared abstract when it is meant to be extended rather than instantiated directly.

This section documents the keywords that introduce these features. For the concepts behind them — inheritance, interfaces, and abstract types — see Object Oriented Programming.

Note

These keywords are recognized only when object-oriented syntax is enabled; otherwise each word is an ordinary identifier. See Enabling Dialects and Features for the flag and dialects reference.

Keywords

Keyword	Description	Support
EXTENDS	Derive a function block type or interface from a base type	Function block: parsed and analyzed; what a derived type inherits is not yet compiled. Interface: parsed only
IMPLEMENTS	Declare that a function block type provides one or more interfaces	Parsed only
ABSTRACT	Mark a function block type as not directly instantiable	Parsed only
INTERFACE	Declare an interface — a named set of method signatures	Parsed only
METHOD	Declare a method on a function block type	Parsed, analyzed, compiled and executed for a method declared on the instance’s own type; a method reached through EXTENDS is not yet compiled
THIS and SUPER	Refer to the instance a method is running on, or to its base type	Parsed only

“Parsed only” means the syntax is accepted and the names it introduces are recognized, but the construct is not yet analyzed or executed — using it reports P9999. Each keyword’s page states exactly what it supports today.