PHP's SPL: Do its interfaces involving arrays cover all array properties?

Question

Would it be possible to write a class that is virtually indistinguishable from an actual PHP array by implementing all the necessary SPL interfaces? Are they missing anything that would be critical?

I'd like to build a more advanced Array object, but I want to make sure I wouldn't break an existing app that uses arrays everywhere if I substituted them with a custom Array class.

Answer 1

The only problems i can think of are the gettype() and the is_array() functions. Check your code for

gettype($FakeArray) == 'array' 
is_array($FakeArray)

Because although you can use the object just like an array, it will still be identified as an object.

Answer 2

In addition to the points made above, you would not be able to make user-space array type hints work with instances of your class. For example:

<?php
function f(array $a) { /*...*/ }

$ao = new ArrayObject();
f($ao); //error
?>

Output:

Catchable fatal error: Argument 1 passed to f() must be an array, object given 

Answer 3

Other differences include the '+' operator for arrays (merging) and the failure of the entire array_* functions, including the commonly used array_merge and array_shift.