PHP __DIR__ 效率

Question

I have a question about the magic variables. Are these true variables or are they a type of function call? Being as how PHP is an interpreted language I am very picky about how I assign variables. I do not like to call a function multiple times if I can store the response in a variable and reuse it without costing the CPU time over and over. Currently, I assign DIR to a local variable and use that variable for all of my includes and anything that requires a current directory path. I am wondering if this is saving CPU time for running a function. I have spent some time looking around the internet but I can't find anything that says how these magic variables are assigned.

example

$dir = __DIR__;

require_once $dir . 'Some Class to Include';
require_once $dir . 'Another Class';

Answer 1

All these "magical" constants are resolved at compile time, unlike regular constants, which are resolved at runtime.

https://www.php.net/manual/en/language.constants.magic.php

So no, you are not saving any CPU time