Implementation of the "private" keyword

Hi!

In the docs it says "The private modifier specifies that the member can only be accessed in its own class."

To me it seems that private (and protected aswelll for that matter) members are only accessable in the same OBJECT rather than the same class.

class A {
    private var _member;
    
    public function initialize(){
        
    }
    
    public function calcMember(){
        _member = doSomeFancyCalculation();
    }
    
    public static function createFromStorage() as A {
        var newA = new A();
        
        // Error: Symbol Not Found Error
        // Details: Could not find symbol '_member'
        newA._member = Storage.getValue("key_storedMember");
        
        return newA;
    }

}

Am I missing something?
This is weird, right?

It makes something like a static factory method very cumbersome to implement.

Let me know if I've missed something here. If not, I think the docs should be updated and this restriction (compared to e.g. java) should be mentioned.

Top Replies

FlowState over 3 years ago +1

Hmm this is pretty interesting. The docs seem wrong here, and the behavior is definitely different from that of C++, C# and Java.
FlowState over 3 years ago in reply to _psx_ +1

_psx_ said:
no, unfortunately is outside the class because you add word static, so it means this function can be called without any object of this class so it's out of privete area

Wow that's interesting…
flogazo over 3 years ago in reply to _psx_ +1

in that case: what would be the point of static functions?

All Replies

jim_m_58 over 3 years ago

With your code and with the "newA" you return, the caller shouldn't be able to access _member.

flogazo over 3 years ago in reply to jim_m_58

it's not about the caller.

The access in line 17 fails. So you can't access A's private member _member from within (a static function of) A.

FlowState over 3 years ago

Hmm this is pretty interesting. The docs seem wrong here, and the behavior is definitely different from that of C++, C# and Java.

peterdedecker over 3 years ago in reply to FlowState

I'd say the docs are right and the implementation is wrong. I'd suggest to file a bug report.

_psx_ over 3 years ago

Everything is OK.

private means privates according to class only class's functions can access privates.

class A

{//<- start private area

//private area where you can access private members and functions

}//end private area

change to:

public var _member;

an will be ok than if you want to access _member outside class's functions

flogazo over 3 years ago in reply to _psx_

you _do_ realize that createFromStorage() is within the class, right?

_psx_ over 3 years ago in reply to flogazo

no, unfortunately is outside the class because you add word static, so it means this function can be called without any object of this class so it's out of privete area

FlowState over 3 years ago in reply to _psx_

_psx_ said:
no, unfortunately is outside the class because you add word static, so it means this function can be called without any object of this class so it's out of privete area

Wow that's interesting, maybe you could explain why the following C++ code compiles and runs without error?

#include <iostream>

class A {
    private:
        int _member;

    public:
        static A *foo() {
            A *newA = new A();
            newA->_member = 42;
            return newA;
        }
        int getMember() {
            return _member;
        }
};

int main() {
    int val = (A::foo())->getMember();
    std::cout << "val = " << val << std::endl;
    return 0;
}

I'm fairly sure similar code in C# and Java would work, as well.

Just because a method is static doesn't mean it isn't part of the class. And as OP said:

flogazo said:
In the docs it says "The private modifier specifies that the member can only be accessed in its own class."

So even if we don't care about other languages or the common understanding of "private", the documentation should reflect how it's actually supposed to work (or vice versa)

jim_m_58 over 3 years ago in reply to FlowState

FlowState said:
Wow that's interesting, maybe you could explain why the following C++ code compiles and runs without error?

Because C++ was always a joke of a language? It was never really OOPS since day 1!

_psx_ over 3 years ago in reply to FlowState

Maybe you are right and maybe in c++/java it runs well but practically there should be no difference between static class function and global function - only one accessing: foo()/class.foo(). And for me as I can't access private members of class from foo() I couldn't access it form static class.foo() too.