PHP Arrays.The Good, the Bad and the Ugly.

Mahesh Gattani

About Me

● Senior Software Engineer at Lucid Software Inc.● Bachelors degree from IIT Delhi, India in Computer Science.● Interests:

○ Sports, not the adventure types. Cricket anyone?○ Long Drives○ Reading

● Follow me on○ methinking.tumblr.com

What are arrays?

PHP arrays: The good.

● Exceptionally easy to use.● No need to allocate memory.● Indexed and associative at the same time.● Different types of keys allows in the same instance.● Ordered.● ...

PHP arrays are not arrays...They are... Ordered Hash Maps

PHP arrays: The bad

PHP arrays are bad because…

● Runtime○ O(n*n) worst case

■ Why you ask? Because they are maps. More about this later.○ Rehashing.

● Memory Usage○ Whole different beast.

UGLY!

Weird, huh!?

Size: 8?Next Free: 6?

Bucket2, Bucket4?● Collisions!

Hashmaps and collisions

PHP hash function● Integers: Integer mod size● Strings: Hash function DJBX33A

PHP DOS Attack by super colliding arrays!

Fixed in 5.3.9

What to do?

Find your use case.

Ex: Judy array

PHP Interfaces

● Array Access○ Interface to provide accessing objects as arrays

● Iterator○ Interface for external iterators or objects that can be iterated

themselves internally.

● Countable○ Classes implementing this can be used with count() function.

Example

SQLiteDBArray

A simple, in memory, indexed array implementation in PHP using SQLiteDB

https://github.com/maheshgattani/SQLiteDBArray

References

● https://sheriframadan.com/2012/10/a-closer-look-into-php-arrays/● http://nikic.github.io/2011/12/28/Supercolliding-a-PHP-array.html● www.php.net● https://github.com/maheshgattani

Thank you!

Lucidchart● Building the next generation of

collaborative web applications.● VC funded, high growth,

profitable.● Graduates from Harvard, MIT,

Stanford● Team has worked at Google,

Amazon, Microsoft.

https://www.lucidchart.com/jobs