Appending to a string is free until someone else holds it
The same .= statement took 0.269 ms and 218.836 ms in two loops that differ by one assignment. What a zend_string costs, where literals live, and why implode is not the fix.
Subject 01 · 8 posts
Internals
The engine: compilation, the Zend VM, memory layout, and the data structures behind the values you pass around.
A property hook emits the same opcode as a plain property
Plain, backed and virtual property reads compile to one identical FETCH_OBJ_R. What separates them is a function call the opcode does not show, measured at nine times.
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.
Two hundred thousand objects, and the collector never ran
Two hundred thousand objects created and dropped, and zero collections. What puts an object in the root buffer, and why the collector's cost is set by what you keep alive.
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.
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.
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.
What happens when PHP runs your code
A request walks from the SAPI to the Zend VM — lexing, compilation to opcodes, the OPcache lookup that skips both, and execution.