[PHP-DEV] [Pre-RFC] Scalar object methods (with a working implementation)

Hi all,

Per Seifeddine's suggestion to keep this out of the karma-request 
thread, I'm opening a pre-RFC discussion for scalar object methods -- 
calling a small, curated set of methods directly on scalar values, e.g. 
$str->trim(), (3)->pow(2). There's a complete, tested implementation and 
a full write-up (links below); I'd like to surface the strongest 
objections before I write the formal RFC.

Disclosure: I built this with an AI assistant (Claude) as a tool. The 
design and the decisions are mine, and I've independently verified the 
engine behaviour, performance, JIT correctness, leak-freedom and the BC 
scan. Flagging it up front for transparency.

I know "methods on primitives" was proposed and declined before 
(Nikita's 2014 "Methods on primitive types in PHP"). The reason it 
stalled was loose typing: $x->trim() would need a runtime type check and 
would behave differently depending on what $x held. This proposal 
sidesteps that entirely, by generalizing the resolution Nikita himself 
suggested in that thread -- requiring an explicit cast where the type 
isn't already clear.

The idea: dispatch only on receivers the compiler already knows are 
scalar. The method call is rewritten at compile time to an ordinary call 
into an internal backing class -- no runtime type dispatch, no new 
opcode, the object method-call path is untouched. A receiver qualifies 
only if its type is guaranteed syntactically: a literal, a 
(string)/(int) cast, a concatenation/interpolation, a non-nullable 
scalar-typed property, or a call with a declared non-nullable scalar 
return type. An untyped $x->trim() is left exactly as today (Error). 
Crucially, dispatch never depends on optimizer-inferred types, so 
behaviour is identical with and without opcache.

     echo "  Hello World  "->trim()->upper();   // "HELLO WORLD"
     echo (3)->pow(2);                          // 9
     echo "hello"->length()->pow(2);            // 25 -- length():int 
chains into the int methods

So the cast Nikita proposed, ((string) $num)->chunk(), is only needed 
where the type isn't already guaranteed; everywhere else the dispatch is 
sound by construction, with no runtime check.

It's intended as one proposal with two independent votes:

1. Scalar methods on guaranteed free receivers (the above). A pure 
capability -- it adds a way to call scalar operations and changes 
nothing about untyped code. Proposed initial sets: a small curated Str 
(trim/upper/lower/length + contains/startsWith/endsWith), Int 
(abs/pow/clamp), and Float (round/ceil/floor/abs); bool deliberately 
gets none (its operations are operators, not methods). The sets are 
governed by explicit criteria and are the easiest thing to tune in 
discussion.

2. Scalar-typed local variables (int $x = ...;, scalar types only), 
which additionally make a typed local a guaranteed receiver (string $s = 
...; $s->trim()). This is the more contested half -- it also carries the 
"local type discipline" argument -- so it's a separate vote: a "no" here 
ships the capability without typed locals.

What I'm deliberately NOT doing, up front so it's not a surprise:

- No method-call-result receivers ($this->getName()->trim()) -- that 
would rest on return-type covariance under inheritance; not worth the 
surface.
- Int::abs/pow return int|float (they can overflow, as the global 
functions do), so they're honest terminals -- they don't chain. 
(Int::clamp is the one initial int method provably :int for all inputs, 
so it does chain.)
- No int|false typed locals -- that's a sentinel state, not a committed 
type; ?T is supported, sentinel-unions are not.
- The backing classes are internal-only (NUL-prefixed name, like 
anonymous classes): class_exists('Str') is false, no Reflection, 
userland "class Str {}" can't collide.

Implementation status -- this is built and tested, not a sketch:

- Scalar methods add zero new opcodes -- the desugar emits an ordinary 
static call, and the object method-call path is byte-for-byte unchanged. 
(Typed locals add dedicated *_TYPED assignment opcodes, but the untyped 
hot path stays byte-identical.)
- Performance (deterministic callgrind, release build): the untyped hot 
path is byte-identical; the standard bench.php suite is +0.145% 
instructions, entirely from predicted-not-taken branches in reference 
opcodes only, with zero added cache misses or branch mispredictions. A 
typed-local write benchmarks at ~0.79x the cost of a typed-property 
write -- a check the language already runs on every typed-property write 
since 7.4.
- References (the objection that sank prior typed-locals attempts) are 
enforced through every path -- =&, by-ref params, 
array/object/static-prop refs, yield, closure capture, $$name, extract, 
$GLOBALS, global -- via the existing typed-property reference machinery. 
Leak-checked under stress.
- Correct under JIT in all three modes (interpreter, function, tracing 
-- differential byte-identical output). opcache SHM + file_cache 
round-trip verified.
- BC impact, measured: an AST scan of the 1,000 most-downloaded 
Packagist packages (173k+ files) found zero method-call sites with a 
guaranteed-scalar receiver -- i.e. zero call sites that change behaviour 
(every such site is a fatal error today). Userland Str classes (incl. 
Laravel's Illuminate\Support\Str) coexist with the backing class, verified.

Full write-up (RFC draft, plus the method-set, performance, and 
BC-impact analyses): 
https://github.com/kralmichal/php-src/tree/rfc/docs/scalar-object-methods-rfc

Implementation branches (PHP 8.6-dev base):
- Primary (scalar methods): 
https://github.com/kralmichal/php-src/tree/rfc/scalar-methods
- Secondary (typed locals, stacked): 
https://github.com/kralmichal/php-src/tree/rfc/typed-locals

What I'd value discussing before I write the formal RFC:

1. Does the "compile-time-guaranteed receivers only" framing actually 
resolve the loose-typing objection, or is there a hole I'm not seeing?
2. The method-set and naming is the most open part -- is a small 
curated, clean-slate set (distinct from the procedural names) the right 
direction, or a non-starter? How should it relate to the existing 
userland efforts in this space (e.g. Psl)?
3. Anything that would sink this before I invest in the full RFC.

Thanks,
Michal Kral