Structural Pattern Matching¶
Structural pattern matching, found in Rust, Haskell, Scala, and OCaml, matches a value against a shape that mirrors the value’s own structure, and simultaneously binds the pieces it finds to new variables. A pattern such as Some(Point { x, y }) both checks that the value is the Some case of an option, wrapping a Point, and extracts x and y in a single step; matches are typically checked exhaustively by the compiler, which rejects code that omits a possible case.
This differs from plain destructuring, which only extracts values assuming the shape is already known to match, and from PHP’s own match expression, which compares a scalar subject against literal values or ranges, but cannot look inside a value’s structure or bind its sub-parts.
PHP has no structural pattern matching: it is being in the works for the future, like PHP 9.0. The match expression compares a value with === against a flat list of candidates; it cannot descend into an array’s or object’s fields, cannot bind sub-values to variables as part of the comparison, and enforces no exhaustiveness over a class hierarchy or enum’s cases beyond throwing UnhandledMatchError at runtime for unmatched inputs. Extracting values still requires a separate destructuring step, such as list assignment, done after the fact and unconditionally.
<?php
// match() compares scalars; it cannot destructure $shape's fields.
$area = match (true) {
$shape instanceof Circle => M_PI * $shape->radius ** 2,
$shape instanceof Rectangle => $shape->width * $shape->height,
default => throw new UnhandledMatchError('unknown shape'),
};
?>
Related : Pattern Matching, Algebraic Data Type, Sum Type, List
