How does PHP 'foreach' actually work?

Let me prefix this by saying that I know what `foreach` is, does and how to use it. This question concerns how it works under the bonnet, and I don't want any answers along the lines of "this is how you loop an array with `foreach`". --- For a long time I assumed that `foreach` worked with the array itself. Then I found many references to the fact that it works with a *copy* of the array, and I have since assumed this to be the end of the story. But I recently got into a discussion on the matter, and after a little experimentation found that this was not in fact 100% true. Let me show what I mean. For the following test cases, we will be working with the following array: $array = array(1, 2, 3, 4, 5); [Test case 1](http://codepad.org/7DIeObk9): foreach ($array as $item) { echo "$item\n"; $array[] = $item; } print_r($array); /* Output in loop: 1 2 3 4 5 $array after loop: 1 2 3 4 5 1 2 3 4 5 */ This clearly shows that we are not working directly with the source array - otherwise the loop would continue forever, since we are constantly pushing items onto the array during the loop. But just to be sure this is the case: [Test case 2](http://codepad.org/nirz6Ufh): foreach ($array as $key => $item) { $array[$key + 1] = $item + 2; echo "$item\n"; } print_r($array); /* Output in loop: 1 2 3 4 5 $array after loop: 1 3 4 5 6 7 */ This backs up our initial conclusion, we are working with a copy of the source array during the loop, otherwise we would see the modified values during the loop. *But...* If we look in the [manual](http://php.net/manual/en/control-structures.foreach.php), we find this statement: >When foreach first starts executing, the internal array pointer is automatically reset to the first element of the array. Right... this seems to suggest that `foreach` relies on the array pointer of the source array. But we've just proved that we're *not working with the source array*, right? Well, not entirely. [Test case 3](http://codepad.org/6n20ooMy): // Move the array pointer on one to make sure it doesn't affect the loop var_dump(each($array)); foreach ($array as $item) { echo "$item\n"; } var_dump(each($array)); /* Output array(4) { [1]=> int(1) ["value"]=> int(1) [0]=> int(0) ["key"]=> int(0) } 1 2 3 4 5 bool(false) */ So, despite the fact that we are not working directly with the source array, we are working directly with the source array pointer - the fact that the pointer is at the end of the array at the end of the loop shows this. Except this can't be true - if it was, then [test case 1](http://codepad.org/7DIeObk9) would loop fore...