PHP delegates

delegates.md

PHP RFC: Delegates

Declaration

To distinguish between classes and delegates a delegate keyword is used to precede delegate name. For FQN optimisations an additional use delegate clause should be placed in all imports and aliases block.

namespace MyApp;

delegate Reducer (?int $sum, int $item = 0): int;

Usage

In methods and functions:

use delegate MyApp\Reducer;

function reduce(array $data, delegate Reducer $callable): int {
  $sum = null;
  foreach ($data as $item) {
    $sum = $callable($sum, $item);
  }
  return $sum;
}

$reducer = fn(?int $sum, int $item = 0): int => ($sum ?? 0) + $item);
$reduced = reduce([10, 22, 34], $reducer);

In properties:

use delegate MyApp\Reducer;

class ArrayReducer
{
  protected delegate Reducer $reducer;
  
  public function __construct(delegate Reducer $reducer)
  {
    $this->reducer = $reducer;
  }
  
  public function reduce(array $data): int
  {
    $sum = null;
    foreach ($data as $item) {
      $sum = $this->reducer($sum, $item);
    }
    return $sum;
  }
}

$reducer = fn(?int $sum, int $item = 0): int => ($sum ?? 0) + $item;
$ar = new ArrayReducer($reducer);
$reduced = $ar->reduce([10, 22, 34]);