New Outer Array Functions Coming to PHP 7.3

PHP 7.3 introduces two new array functions for working with the “outer” keys of an array. The RFC proposal included four new functions for both keys and values, but only the array key functions were accepted:

• array_key_first() (accepted)
• array_key_last() (accepted)
• array_value_first() (declined)
• array_value_last() (declined)

Although the outer array value functions were declined, at least new functions will be available for getting the outer keys of an array.

New Accepted Array Key Functions

First, let’s look at the array_key* functions. These functions allow you to get the first and last key respectively.

For an associative array, here’s an example:

$array = ['a' => 1, 'b' => 2, 'c' => 3];
 
$firstKey = array_key_first($array);
$lastKey = array_key_last($array);
 
assert($firstKey === 'a');
assert($lastKey === 'c');

And for a numeric array:

$array = [1 => 'a', 2 => 'b', 3 => 'c'];
 
$firstKey = array_key_first($array);
$lastKey = array_key_last($array);
 
assert($firstKey === 1);
assert($lastKey === 3);

Finally, for an empty array the functions return null:

$array = [];
 
$firstKey = array_key_first($array);
$lastKey = array_key_last($array);
 
assert($firstKey === null);
assert($lastKey === null);

Declined Array Value Functions

I’d want to emphasize again, the array value functions were not accepted with 18 “no” votes and only 15 “yes” votes with the vote requiring a simple majority

I bet that you can almost predict how these would work without seeing any examples, which is awesome to me!

First, let’s look at an example of getting the first and last values of an associative array:

$array = ['a' => 1, 'b' => 2, 'c' => 3];
 
$firstValue = array_value_first($array);
$lastValue = array_value_last($array);
 
assert($firstValue === 1);
assert($lastValue === 3);

Next, an example of getting the outer values of a numeric array:

// usage of a numeric array
$array = [1 => 'a', 2 => 'b', 3 => 'c'];
 
$firstValue = array_value_first($array);
$lastValue = array_value_last($array);
 
assert($firstValue === 'a');
assert($lastValue === 'c');

Last, the outer values of an empty array will return null:

$array = [];
 
$firstValue = array_value_first($array);
$lastValue = array_value_last($array);
 
assert($firstValue === null);
assert($lastValue === null);

I am not entirely sure why this vote failed, but I suspect from the GitHub comments that one reason might be concern that the null return value for an empty array is ambiguous.

Conclusion

It’s kind of interesting to me that PHP doesn’t already have a method for doing these things as of version seven of the language, and it’s nice to see at least the acceptance and implementation of array_key_first() and array_key_last(), even if the value functions were declined.

You can learn more about the array key RFC and check out the PHP 7.3 implementation of the array_key_* functions on GitHub.