C implementation of the CFunction primitive. An IoCFunctionData holds a C function pointer (IoUserFunction: target/locals/message -> result), an optional typeTag gate (only activate if target's tag matches, else raise a typed error), a uniqueName symbol for introspection, and profiler timing. Like Block, CFunction is self-activating: the tag's activateFunc is IoCFunction_activate, so fetching a CFunction from an activatable slot calls through immediately. This is how every C-backed Io method (List append, Number +, Object if/while/for, etc.) is installed — IoObject_addMethodTable_ creates one CFunction per entry and stores it in the target proto. CFunctions do not pre-evaluate their arguments; the recipient uses IoMessage_locals_valueArgAt_ or the pre-eval fast path (IoState_preEvalArgAt_) to fetch them lazily.
Tag dispatch entry point: validates that the target's tag matches the CFunction's optional typeTag (raising a VM error on mismatch) then invokes the stored C function pointer with (target, locals, message). Unlike IoBlock_activate there is no fresh locals object — the C function inspects the caller's locals and the message directly, which is why CFunctions can be cheap. The commented-out retain-pool pair is a historical concern; pools are managed by callers today.
Profiler-enabled wrapper around IoCFunction_activate. setProfilerOn(true) swaps this in as the tag's activateFunc so every call accumulates elapsed clock() time into the CFunction's profilerTime.
Registered as the tag's freeFunc. Frees the IoCFunctionData payload. The uniqueName symbol is interned on state and GC-managed.
Registered as the tag's markFunc. Only the uniqueName symbol is a GC root — the C function pointer and typeTag are not IoObjects.
Builds the CFunction tag and wires clone/mark/free plus — crucially — activateFunc, which is what makes CFunctions self-executing when looked up through a slot.
Primary constructor used by IoObject_addMethodTable_: clones the CFunction proto and stamps in the C function pointer, the optional type gate (tag), and the uniqueName symbol for introspection. Every entry in a C method table produces one of these.
Debug printer dumping pointer, C function pointer, owning type name, and uniqueName. Called from diagnostic paths only; not part of the Io-visible print protocol.
Creates the CFunction proto with a zeroed IoCFunctionData whose func points at IoObject_self (the identity function) as a safe default. The proto is not marked activatable — only its clones are, so the proto itself can be fetched via getSlot. IoCFunction_protoFinish adds the method table later once prerequisite protos exist.
Deferred init: installs the Io-visible method table on the CFunction proto after the Symbol/Sequence protos exist (method registration needs IOSYMBOL to work). Called late in IoState_init so earlier proto construction can use CFunctions without forcing a circular init order.
Registered as the tag's cloneFunc. Copies the proto's data block and flips isActivatable on — this is the point at which a CFunction becomes self-executing when placed in a slot.