Question

I have a set of objects I want to put into an array and I want to distinguish them with keys.

The initial code I wrote was:

array_push($array[$key], new myObj(param1, param2, etc));

When I run it I get the warning:

PHP Warning:  array_push() expects parameter 1 to be array, null given in file.php on line 56

I added a var_dump() to see what was actually happening and it was filling the array with each element ‘$key => null’ as suggested by the error.

If I remove the [$key] from the line then it fills the array with instances of myObj as expected so I know that the constructor is functioning correctly and not really returning ‘null’.

Answer 1

Keys in associative arrays need to be unique, so if you want to keep the notion of a key/value pair where you can access things directly by the key, don’t use array_push, simply set the key (this is fine to do in PHP):

$array[$key] = new myObj(param1, param2, etc)

On the other hand, if you want to have a list of key/value pairs, like a stack, and you’re adding just one key/value pair at a time, don’t use array_push, simply add to the array using PHP’s shorthand syntax (as the manual says, this is faster as it saves you a function call):

$stack[] = array($key => new myObj(param1, param2, etc));

One more possibility, if you have a bunch of key/value pairs, and you want to add all of them to some stack like structure (but not be able to index directly by some key), then you should use array_push:

array_push($stack,
    array($key1 => new myObj(param1, param2, etc)),
    array($key2 => new myObj(param3, param4, etc))
);