internals
A declared property is cheaper than an array key
One hundred thousand four-field records cost 143.54 bytes each as objects and 397.14 as associative arrays. Where the crossover is, and what one undeclared property costs.
hashtable
4 posts
internals
A by-reference foreach leaves a reference in every element
Walking an array with foreach ($rows as &$row) wraps every element in a zend_reference. On a million integers that is 32 MB the loop never gives back.
internals
What a PHP variable actually is
A zval is sixteen bytes, a value union and a type tag. What that tag says decides whether an assignment copies anything, what a reference costs, and which variable pays.
internals
PHP arrays are not arrays
One structure serves as list, dictionary and set. Packed and hashed layouts, what each costs in memory, and when a conversion happens.