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Why objects (usually) use less memory than arrays in PHP

Because the properties for the object are predefined PHP no longer has to store the data in a hashtable, but instead can say that $foo is property 0, $bar is property 1, $baz is property 2 and then just store the properties in a three-element C array.

This means that PHP only needs one hashtable in the class that does the property-name to offset mapping and uses a memory-efficient C-array in the individual objects. Arrays on the other hand need the hashtable for every array.


Freek Van der Herten is a partner and developer at Spatie, an Antwerp based company that specializes in creating web apps with Laravel. After hours he writes about modern PHP and Laravel on this blog. When not coding he’s probably rehearsing with his kraut rock band.