同じメソッドで foreach も each(function) もできるようにする例

eachlize.php

<?php

class R {
    private $begin;
    private $end;

    public function __construct($begin, $end) {
        $this->begin = $begin;
        $this->end = $end;
    }

    public function each(callable $closure = null) {
        return self::eachlize(function () {
            for ($i=$this->begin;$i <= $this->end; ++$i) {
                yield $i;
            }
        }, $closure);
    }

    public static function eachlize(callable $each, callable $callback = null) {
        if ($callback === null) {
            return $each();
        }

        foreach ($each() as $v) {
            $callback($v);
        }
    }
}

$r = new R(1,3);

foreach ($r->each() as $v) {
    echo $v;
}
echo "\n";

$r->each(function($v) {
    echo $v;
});
echo "\n";

output

$ php eachlize.php
123
123