Developing with JRuby Truffle

Code patterns

Where to allocate helper nodes (a node used in another node)

• If the node does not use the DSL, either allocate eagerly if the node is always used, or lazily if it is only used in some cases.
• If the node is used by every specialization: allocate the helper node eagerly as a @Child.

public abstract class MyNode extends RubyNode {
    @Child MetaClassNode metaClassNode;

    public MyNode(RubyContext context, SourceSection sourceSection) {
        super(context, sourceSection);
        metaClassNode = MetaClassNodeGen.create(context, sourceSection, null);
    }
...

• If the node is used by only one specialization: use @Cached.

        @Specialization
        public long objectID(DynamicObject object,
                @Cached("createReadObjectIDNode()") ReadHeadObjectFieldNode readObjectIdNode) {
            final Object id = readObjectIdNode.execute(object);
            ...
        }

        protected ReadHeadObjectFieldNode createReadObjectIDNode() {
            return new ReadHeadObjectFieldNode(Layouts.OBJECT_ID_IDENTIFIER);
        }

However, if the nodes already uses @Cached and there are guards on the @Cached values, consider whether you want one node per Specialization instantiation or only one for the whole node.

• Otherwise use the lazy pattern which includes the call on the node.

        @Child ToStrNode toStrNode;
        ...

        protected DynamicObject toStr(VirtualFrame frame, Object object) {
            if (toStrNode == null) {
                CompilerDirectives.transferToInterpreterAndInvalidate();
                toStrNode = insert(ToStrNodeGen.create(getContext(), getSourceSection(), null));
            }
            return toStrNode.executeToStr(frame, object);
        }

If you want to call different methods on a node, then use a getStrNode() helper which returns the node.