see comments in the code below. they are my questions.

But feel free to ignore the comment about 'private(this)' ;-)


interface Ship
{
    @safe void setSpeed(int speed);
    @safe int getSpeed();
}

class PirateShip : Ship
{
    private int speed = 0; // If only I had 'private(this)' !!

    // how do I know this method is actually an implementation of an interface method
    // and not a method specific to this class?
    public void setSpeed(int speed)
    {
        this.speed = speed;
    }

   // how do I know this method is actually an implementation of an interface method
   // and not a method specific to this class?
   public int getSpeed()
    {
        return speed;
    }
}


class MerchantShip : Ship
{
    private int speed = 0; // If only I had 'private(this)' !!

    // how do I know this method is actually an implementation of an interface method
    // and not a method specific to this class?
    // AND ... how come I can change a @safe interface method into a @trusted one?
    public @trusted void setSpeed(int speed)
    {
        int *s = void; // Mmmm.. and my interface all had @safe methods!!
        this.speed = speed;
    }

    // how do I know this method is actually an implementation of an interface method
    // and not a method specific to this class?
    // AND ... how come I can change a @safe interface method into a @trusted one?
    public @trusted int getSpeed()
    {
        int *s = void; // Mmmm.. and my interface all had @safe methods!!
        return speed;
    }

}