当其他类使用它时，哪个时候php中的一个类中的常量变量被加载到RAM中？

Question

For example I have class A in file a.php

namespace Path\To;
class A {

    const SOME_VAR = 'value';

    // many functions
}

And I have class B in file b.php

use Path\To\A;
class B {

    public function foo() {

        $i = 1;
        $i = 2;
        $i = 3;
        // other code

       $someVar = A::SOME_VAR;

    }

    // other functions
}

Which time in executing function foo constant variable SOME_VAR loads in RAM. On first line of function foo or on line $someVar = A::SOME_VAR; or line use Path\to\A; or elsewhere?

Answer 1

a.php is read, parsed and executed when $someVar = A::SOME_VAR; is executed inside b.php. That is also when the 'value' string is loaded into memory.

At that same time, everything about class A is loaded. If you where to add const SECOND_VAR = 'another-value'; to class A, once $someVar = A::SOME_VAR; has been executed there is also a bit of RAM that contains 'another-value'.

What the use Path\To\A; line does, is just tell PHP "if class A is requested, what they mean is \Path\To\A". You can add use Some\Non\ExistentClass and use Some\Class\That\Has\ASyntaxErrorInTheCode, and nothing will change, because as long as you don't try to actually do anything with ExistentClass or ASyntaxErrorInTheCode PHP will never read the files that those classes are in.