从对象迭代数组

Question

I want to perform some magic so that when I try to iterate over an object I will actually iterate over an array from within the object. Something like a getter for loops.

class A {
    protected $array = [1,2,3];

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

$a = new A;

foreach($a as $value) {
   echo $value;
}

// output should be "123"

Not even sure that this is possible but I suspect I should be using ArrayObject but it is not very straightforward for me, I can't figure out how to make it do this.

Please note : I could define a getter method and loop over $a->getArray() but that is not what I want to do. Thank you.

Answer 1

You can implement the Iterator interface . To do that, you need to implement a couple of methods in your object, which you can redirect to your array:

<?php

class A implements Iterator {
    protected $array = [1,2,3];

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

    public function rewind()
    {
        reset($this->array);
    }

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

    public function key() 
    {
        $key = key($this->array);
        return $key;
    }

    public function next() 
    {
        $value = next($this->array);
        return $value;
    }

    public function valid()
    {
        $key = key($this->array);
        return $key !== null && $key !== false;
    }    
}

$a = new A;

foreach($a as $value) {
   echo $value;
}

Of course you can implement your own method of keeping track of the 'current' item, but since an array does that already, it's as easy to let it do it for you, and methods like rewind just call array functions.

Answer 2

Rather than writing all the boilerplate to make this an iterable object, you could use a generator:

class A {
    protected $array = [1,2,3];

    public function __foriteration() {
        foreach($this->array as $value) {
            yield $value;
        }
    }
}

$a = new A;

foreach($a->__foriteration() as $value) {
   echo $value;
}