Skip to content

RFC.md

Latest commit

 

History

History
96 lines (70 loc) · 3.29 KB

RFC.md

File metadata and controls

96 lines (70 loc) · 3.29 KB
Raw

PHP RFC: apply builder blocks (lambda-with-receiver)

  • Version: 0.1
  • Date: 2026-07-10
  • Author: Edd Mann the@eddmann.com
  • Status: Draft
  • Target: PHP 8.5 (experimental fork)
  • Implementation: feature.patch

Introduction

Building and configuring an object in PHP means either a fluent interface (every method must return $this), a constructor with many arguments, or a sequence of $obj->… statements naming the variable over and over. Borrowing Kotlin's apply — a function literal with receiver — this RFC adds a block in which $this is the object being built and the block evaluates to that object.

Proposal

apply (EXPR) { STMTS }
  • STMTS run with $this bound to EXPR.
  • Surrounding variables are captured by value (arrow-function semantics).
  • The expression evaluates to EXPR (the receiver).
$config = apply (new Config()) {
    $this->debug = $debug;
    $this->cache = apply (new Cache()) {   // nested: $this is the Cache
        $this->ttl = 300;
    };
};

This is the object-building member of Kotlin's scope-function family (apply, which returns the receiver). It composes for tree-shaped construction — DOM/HTML builders, configuration objects, test fixtures.

Design

apply is a semi-reserved keyword. The block lowers to a self-invoking closure bound to the receiver:

(function () { STMTS; return $this; })->call(EXPR)

Closure::call() binds $this and returns the closure's result ($this), so the expression yields the receiver. The synthesised closure is marked so the compiler runs the arrow-function implicit-capture pass over it, importing free variables by value without a use list. There is no new opcode and no new runtime class; the entire feature is a front-end desugar.

Backward Incompatible Changes

  • apply becomes a semi-reserved keyword (still usable as a method/constant name).
  • No change to existing programs that do not use apply.

Scope / Future Scope

  • Object receivers only. Closure::call() requires an object $this; a scalar receiver is a TypeError.
  • Returns the receiver (Kotlin apply). A with / run variant returning the block's own last value is possible future work.
  • Explicit $this-> for member access. Kotlin's implicit receiver (bare child { … } meaning this.child { … }) is future scope.
  • Like match, an apply block must be parenthesised to be dereferenced ((apply (…) { … })->method()).

RFC Impact

  • Opcache: no new opcode. The desugar emits an ordinary closure and a method call, both cached as usual.
  • Tokenizer: adds T_APPLY (exposed to token_get_all() / token_name()).

Proposed PHP Version(s)

Next PHP 8.x minor.

Proposed Voting Choices

Yes/No, 2/3 majority.

Patches and Tests

  • feature.patch; tests/: $this binding, receiver return, by-value capture, nesting, control flow in the block, method-context receiver, parenthesised dereference, single receiver evaluation, exception propagation, and the semi-reserved name.

References