Object-oriented extensions

Object-oriented extensions

IEC 61131-3 third edition (2013) introduced an object-oriented layer on top of the FUNCTION_BLOCK POU: classes can declare methods, interfaces describe contracts, and FBs can extend a base FB or implement an interface. The third edition also defined access-modifier visibility (PUBLIC / PRIVATE / PROTECTED / INTERNAL), the THIS / SUPER self-references, properties with GET / SET accessors, the ABSTRACT / FINAL / OVERRIDE modifiers, namespaces, and reference types.

ForgeIEC’s parser (tree-sitter-st) is being extended to cover the OOP layer ahead of the codegen pipeline that emits it. matiec does not implement any of these constructs — when ForgeIEC’s codegen target is c (matiec/iec2c, deprecated since Phase 6 of the ST→C++-Codegen-Sprint), POUs using OOP fail to compile. With the C++-codegen pipeline (target = "cxx", default since Phase 5), OOP support is on the roadmap but not yet emitted.

Refer to the individual pages for the current status of each construct.

Pages

• METHOD / END_METHOD — declare a method on a FUNCTION_BLOCK. Methods carry their own VAR-block and signature; they are called with <fb_instance>.<method>(...) syntax.
• INTERFACE / END_INTERFACE — declare a contract of method signatures that conforming FBs must implement. Interfaces enable polymorphic dispatch via interface-typed variables.
• EXTENDS — single inheritance between FUNCTION_BLOCKs. The derived FB inherits the base’s members and methods, may override methods, and gains access to the base via SUPER.
• IMPLEMENTS — declare that a FUNCTION_BLOCK conforms to one or more interfaces. Compiler enforces that every interface method is implemented with a matching signature.

Out-of-section but related

The following OOP-adjacent constructs live on other pages:

• THIS / SUPER — implicit references inside methods. Documented on the METHOD page.
• ABSTRACT / FINAL / OVERRIDE — method/class modifiers. Documented on the METHOD and EXTENDS pages.
• PUBLIC / PRIVATE / PROTECTED / INTERNAL — visibility modifiers. Documented in variable-declarations/ (TBD — separate page once tree-sitter-st emits the tokens).
• PROPERTY / GET / SET — property accessors. Future page, currently a stub in the chapter-map.
• NAMESPACE / END_NAMESPACE / USING / :: — namespace declarations and the scope-resolution operator. Future page.
• REFERENCE / REF_TO / REF= / NULL — reference types for OOP polymorphism. Future page.

IEC reference

IEC 61131-3 third edition (2013), clauses 6.5.3 (METHOD), 6.5.4 (INTERFACE), 6.5.5 (EXTENDS / IMPLEMENTS), 6.5.6 (THIS / SUPER), 6.5.7 (Properties), 6.5.8 (visibility / modifiers).

ForgeIEC roadmap

The TS-ST-Cleanup Phase 2 sprint adds the OOP tokens to the parser. Once the parser sees them, the AST-walker is extended with OO-aware IR nodes, the emitter learns to map them to C++ classes/inheritance/virtual-dispatch, and these pages become implementation reference instead of roadmap pages.