D: Modules and Class Private Members

One of D’s major differences from C++ is to do with classes and their private members.

In D, any code in the same module as a class can access that class’ private members.  An example is probably useful:

module example.Dogsarama;

class Dog
{
public:

    this(int age)
    {
        m_age = age;
    }

    int Age()
    {
        return m_age;
    }

    void SetAge(int age)
    {
        m_age = age;
    }

private:

    int m_age;
}

void SetDogAge(Dog d, int age)
{
    // I can access this dog's privates!!!
    d.m_age = age;
}

Because SetDogAge() is part of the same module as the Dog class, it is entitled to access and manipulate Dog’s private members.

So in another module we can do this:

module example.Main;

import std.stdio;
import example.Dogsarama;

int main(char[][] args)
{
	auto fido = new Dog(15);

	SetDogAge(fido, 17);

	writeln(fido.age());

	return 0;
}

Though I had read the main parts of the D spec I only discovered this by experimenting.  I later found the appropriate documentation which is unfortunately a bit obscure, IMO.