How to set methods private to module?

Question

I have two D classes in one module. I would like class A to have a property, which can only be accessed from class A and class B. How would I do this?

class A {
    int a = 5; // Make this accessible to, and only to, B. 
}

class B {
    this(in A pA) {
        int b = pA.a;
    }
}

Answer 1

private is private to a module, not a class. So, marking a symbol as private makes it so that only stuff in that module can access it.

package makes it so that only stuff in the same package can access the symbol.

protected makes it so that only stuff in that class and in classes derived from that class can access the symbol (unlike the others, protected makes no sense outside of classes).

public makes it so that anything can access the symbol.

private and package functions are never virtual, whereas protected and public functions are always virtual unless the compiler is able to determine that they don't need to be (which at this point, can pretty much only happen when the function is final and doesn't override a function in a base class).

So, as long as your two classes are in the same module, and their members are private, they can access each others members - as can anything else within the module - but nothing outside the module can access them. There is no way to restrict access within a module except for when the symbol is local to a function, so if you want to make it so that one class cannot access the members of another, then you're going to need to put them in separate modules.

Answer 2

just add private

the access modifiers are module based with protected as the only exception

http://dlang.org/attribute.html#ProtectionAttribute (emph mine)

Private means that only members of the enclosing class can access the member, or members and functions in the same module as the enclosing class. Private members cannot be overridden. Private module members are equivalent to static declarations in C programs.