late-static-binding.md

Late static binding

PHP's static:: resolves to the called class at runtime, not the class that lexically defines the method. Manticore has no runtime metadata and monomorphises aggressively, so LSB is implemented the same way: per-descendant method copies, the called class threaded as a compile-time scope and the right copy selected at each call site.

What it covers

• static::class → the called class name as a string.
• new static() → instantiate the called class.
• static::method(...) → dispatch to the called class's override.
• static::$prop / static::CONST → the called class's static member.
• parent::m() / self::m() forward the scope (a downstream static:: stays bound to the original called class).
• Constructors: new C() runs an inherited ctor with static == C.

Mechanism

For an LSB method M owned by class R, every strict descendant S of R gets a specialised copy named R__M__lsb<S> whose static:: resolves to S. The normal R__M copy serves the S == R case.

• Lowering (LowerFromAst): currentStaticClass is the scope, distinct from currentLowerClass (the lexical/defining class, which still drives self::, parent::, property layout). resolveStaticClass('static') returns the scope. A method is flagged LSB (sawStaticUse) when it references static or makes a forwarding self::/parent::/static:: call. Flagged methods are queued (LsbPending) and, once the whole class table is known, emitLsbSpecializations re-lowers each body once per descendant via the shared lowerMethodFn helper.
• StaticCall_.staticClass carries the forwarded scope separately from the dispatch target, so parent::m() dispatches to the parent but keeps the called class.
• Dispatch (EmitLlvm): lsbTarget(owner, method, scope) returns owner__method__lsb<scope> when that specialisation exists, else the plain owner__method. Static calls and new use the statically-known scope; instance calls feed the runtime class into the existing class_id virtual switch (each case is one concrete class → one scope), so an inherited LSB method becomes polymorphic even with no override.

Cost & limits

• Code growth is bounded by (LSB methods) × (descendants); negligible in practice — the self-host binary size is unchanged.
• get_class($this) still returns the static type, not the runtime class — use static::class. Tracked in docs/ROADMAP.md Tier 1.