Re: [RFC] Normalize array's "auto-increment" value on copy on write

On Thu, 20 Jun 2019 at 13:11, Wes <netmo.php@gmail.com> wrote: > I left that out of scope for the RFC, for reasons I don't have the > knowledge to describe properly. In the following example, > unset() should > reset the auto increment to 1 only after the third > unset() call > > ``` > $array = [0, 1, 2, 3]; // auto increment is 4 because there are "holes" in > the index > unset($array[1]); // auto increment is still 4 > unset($array[2]); // auto increment is still 4 > unset($array[3]); // auto increment is 1, because the index sequence is > contiguous, without holes > ``` > I wonder if it would be possible (and sufficient) to detect if the element being removed was the highest key, and only then look for the new "next" value. The new value can be found either by decrementing the known value until you hit an existing entry (optimal for large arrays with few gaps in the sequence of keys) or by checking all the keys and finding the max (optimal for small but sparse arrays like [12, 145, 65546]). # pseudocode: if ( key_being_unset == array.next_key - 1 ) { if ( short_or_likely_to_be_sparse(array) ) { new_highest_key = max(array.keys); } else { # Find highest unused number, starting from the one just deleted do { new_highest_key = key_being_unset - 1; } while ( not key_exists(array, new_highest_key) ); array.next_key = new_highest_key + 1; } } I've no idea if this is plausible or not. Regards, -- Rowan Collins [IMSoP]