Ruby-like iterators in PHP

I’ve started playing with Ruby recently, and one of the things that got my attention in Ruby were iterators. They are different inside from regular loops but work in a similar way, and looks like people (at least ones that write tutorials and code examples 😉 ) like to use them. For example, you can have:

arr = {"one" => 1, "two" => 2, "three" => 3}
arr.each do |key, val|
print "#{key}: is #{val}\n"
end

which iterates over a Ruby hash and prints:

three: is 3
two: is 2
one: is 1

So it got me thinking – suppose I wanted to do something like this in PHP (suppose I don’t like regular loop-y iterators for some weird reason). Naturally, I wouldn’t get it in the same concise form as Ruby does, since I can’t change the syntax. But I could get the essence. Let’s try it. First, the main iterator:

class RubyIterator {
  protected $_body;

  public function __construct($body) {
    if(!is_callable($body)) {
      throw new Exception("Iterator body should be a callable");
    }
    $this->_body = $body;
  }
  public function yield()
  {
    $args = func_get_args();
    call_user_func_array($this->_body, $args);
  }
}

Next, less try to make some class that uses it:

class RubyArray {
    protected $_arr;
    public function __construct(array $a)
    {
        $this->_arr = $a;
    }

    public function each($body) {
        $iter = new RubyIterator($body);
        foreach($this->_arr as $k => $v) {
            $iter->yield($k, $v);
        }
    }
}

and then:

/*
arr = {"one" => 1, "two" => 2, "three" => 3}
arr.each do |key, val|
    print "#{key}: is #{val}\n"
end
*/
    
$arr = new RubyArray(array("one" => 1, "two" => 2, "three" => 3));
$arr->each(function($key, $val) { echo "$key: is $val\n"; });

and the result the same, of course. Or, let’s try with ranges:

class RubyRange {
    protected $_from, $_to;
    public function __construct($from, $to) {
        $this->_from = $from;
        $this->_to = $to;
    }
    public function each($body) {
        $iter = new RubyIterator($body);
        for($i=$this->_from; $i<=$this->_to; $i++) {
            $iter->yield($i);
        }
    }
    
}

and use it:

/*
r = 1..10;
r.each do |i|
    print "#{i*i}\n"
end
*/

$rr = new RubyRange(1, 10);
$rr->each(function($i) { echo $i*$i."\n"; });

which indeed produces:

1
4
9
16
25
36
49
64
81
100

And so on – if one wanted, whole set of iterator methods could be implemented (I’m of course too lazy to do that 🙂 ). I wonder if there are use cases that we can’t do there.