PHP generators

generators-vs-iterator.php

<?php

// Data on which we operate

$tree=[
    '+'=>[
        '*'=>[1,2],
        '-'=>[
            '+' => [3,4]
            , 5
        ]
    ]
];

// Implementation using corroutines
function iterateTreeLeafs($tree)
{
    if(is_array($tree)){
        foreach($tree as $child){
            $subs=iterateTreeLeafs($child);
            foreach($subs as $sub){
                yield $sub;
            }
        }
    }else{
        yield $tree;
    }
}

// Implementation using Iterators
class ExprIterator implements Iterator
{
    private $stack=[];
    private $current;
    private $valid=true;

    public function __construct($data)
    {
        array_push($this->stack,$data);
    }

    public function current()
    {
        return $this->current;
    }

    public function next()
    {
        $this->valid=!empty($this->stack);
        $item = array_pop($this->stack);
        if(is_array($item)){
            while(is_array($item)) {
                $item=array_reverse($item);
                foreach($item as $i){
                    array_push($this->stack,$i);
                }
                $item = array_pop($this->stack);
            }
        }
        $this->current=$item;
    }

    public function key()
    {
        return null;
    }

    public function valid()
    {
        return $this->valid;
    }

    public function rewind()
    {

    }
}

// Usage of both implementation
$generator=iterateTreeLeafs($tree);
foreach($generator as $leaf)
{
    echo $leaf;
}

$iterator=new ExprIterator($tree);
foreach($iterator as $leaf)
{
    echo $leaf;
}