static class

[Steven Schveighoffer]

On Sun, 17 Feb 2013 18:26:37 -0500, Ben Davis <entheh at cantab.net> wrote:

> On 17/02/2013 22:25, Jonathan M Davis wrote:
>> On Sunday, February 17, 2013 23:00:19 Michael wrote:
>>>> That's not the meaning of static in that context.
>>>
>>> As I understand a static class can't be instantiated.
>>
>> I have no idea how you came to that conclusion.
>
> In fairness, it is the natural guess you'd make if you haven't actively  
> used nested instance classes and understood how the outer instance  
> pointer is stored. We use Java at work (same mechanism as D), and hardly  
> anyone actually knows to write 'static' when they create a nested class  
> that they intend to be POD. :)

static class at module level means nothing.  It's a noop.

static class inside a class means, this class instance does not contain a  
pointer to it's outer class instance, nor does it have access to the outer  
class instance's variables (naturally).

so:

module X;

static class A {}

is exactly equivalent to

class A {}

> You can make as many nested instances as you like.

Yes, as Jonathan indicated, this is possible.

> Is it possible to write someInstanceOfR.outer? I've occasionally wanted  
> Java to have that feature, and ended up storing the 'outer' reference  
> manually. Though this probably means I was writing bad code; I can't  
> remember. :D

I don't know if outer is public or private.  Quick test...

Yep, you can access it.  But I don't know if that is the correct way to do  
it, or if that is intended.  The spec does not consider that possibility.

I will note, one VERY annoying thing about outer, is that outer by itself  
doesn't work inside an inner class' function unless you qualify it with  
this:

class A
{
    int x;
    class B
    {
       void foo()
       {
          // outer.x = 5;  // Error: undefined identifier outer
          this.outer.x = 5; // ok
       }
    }
}

-Steve