How is the presence of a single object in the current file achieved in a generator?

In PHP, a generator is achieved by returning a Generator object from a generator function.

A function declared with the yield keyword automatically becomes a generator. When such a function is called for the first time, PHP does not execute its code immediately. Instead, it returns an object of type Generator, which encapsulates the state of the function's execution.

This Generator object acts as an iterator. Every time the Generator object is iterated over (for example, in a foreach loop or using methods like next(), send(), current(), etc.), PHP resumes execution of the generator code from where it left off after the last yield statement.

The yield operator pauses the function execution and returns a value. When the next value is requested, execution resumes from the statement following the yield.

Thus, even though a generator function may contain multiple yield statements, it creates and returns only one instance of a Generator object on the first call. This single object manages the state of the generator's execution and provides access to the generated values.

<?php
function simple_generator() {
    yield 1;
    yield 2;
    yield 3;
}

$generator1 = simple_generator(); // Creates one Generator object

// Both objects $generator1 and $generator2 refer to the same type of Generator object
// But each call to simple_generator() creates a *new* instance of a Generator object
$generator2 = simple_generator();


echo get_class($generator1); // Outputs Generator

// $generator1 and $generator2 are different instances
var_dump($generator1 === $generator2); // Outputs bool(false)
?>

The key idea is that a generator function, when called, does not execute its code but creates and returns a generator object, which is then used for step-by-step execution of the generator's logic.