I have a class called Collection which stores objects of same type.
Collection implements array interfaces: Iterator, ArrayAccess, SeekableIterator, and Countable.
I'd like to pass a Collection object as the array argument to the array_map function. But this fails with the error
PHP Warning: array_map(): Argument #2 should be an array
Can I achieve this by implementing other/more interfaces, so that Collection objects are seen as arrays?
The array_map() function doesn't support a Traversable as its array argument, so you would have to perform a conversion step:
array_map($fn, iterator_to_array($myCollection));
Besides iterating over the collection twice, it also yield an array that will not be used afterwards.
Another way is to write your own map function:
function map(callable $fn)
{
$result = array();
foreach ($this as $item) {
$result[] = $fn($item);
}
return $result;
}
Update
Judging by your use-case it seems that you're not even interested in the result of the map operation; therefore it makes more sense to use iterator_apply().
iterator_apply($myCollection, function($obj) {
$obj->method1();
$obj->method2();
return true;
});
array_map wants, as the name suggests, arrays. It's not called iterator_map after all. ;)
Apart from iterator_to_array(), which produces a potentially large temporary array, there's no trick to make iterable objects work with array_map.
The Functional PHP library has a map implementation which works on any iterable collection.
If you're not interested in creating a new array that is a function mapped over the original array, you could just use a foreach loop (because you implement Iterator).
foreach($item in $myCollection) {
$item->method1();
$item->method2();
}
if you actually want to use map, then I think you'll have to implement your own. I would suggest making it a method on Collection, eg:
$mutatedCollection = $myCollection->map(function($item) {
/* do some stuff to $item */
return $item;
});
I would ask yourself if you really want to use map or do you really just mean foreach
I came up with the following solution:
//lets say you have this iterator
$iterator = new ArrayIterator(array(1, 2, 3));
//and want to append the callback output to the following variable
$out = [];
//use iterator to apply the callback to every element of the iterator
iterator_apply(
$iterator,
function($iterator, &$out) {
$current = $iterator->current();
$out[] = $current*2;
return true;
},
array($iterator, &$out) //arguments for the callback
);
print_r($out);
This way, you can generate an array without iterating twice as you would to with the approach like:
$iterator = new ArrayIterator(array(1,2,3));
$array = iterator_to_array($iterator); //first iteration
$output = array_map(function() {}, $array); //second iteration
Good luck!
I just stumbled upon this question and I managed to cast the collection to an array to make it work:
array_map($cb, (array) $collection);
disclaimer For the original question this might not be a suitable option but I found the question while looking to solve a problem which I solved with this solution. I would recommend using a custom iterator map where possible/viable.
another option is to do something like this:
foreach($collection as &$item) {
$item = $cb($item);
}
which will mutate the underlying collection.
EDIT:
It has been pointed out that casting to an array can have unwanted side effects. It would be better to add a method to your collection to return the array from the iterator, and traverse that, or otherwise add a map method which accepts a callback and run a loop on the underlying iterator.
