Error: 'this' is only defined in non-static member functions

Jacob Carlborg doob at me.com
Thu Nov 23 09:32:38 UTC 2017


On 2017-11-23 01:35, Jonathan M Davis wrote:

> It would make sense with something like the nodes of a linked list if they
> needed access to the container for some reason. Pretty much any case where a
> an instance of a nested class is going to be associated with a specific
> instance of its parent class and needs access to it would be a canditate.
> It's not that uncommon to see cases in C++ or Java where you'd pass a
> pointer to the "parent" to an instance of a nested class when it's created,
> and having outer built-in is kind of like that.
> 
> Personally, I've never had a use for it. I don't even use classes much in D,
> since I rarely need inheritance. And as I understand it, most D programs
> don't use classes very heavily for that very reason. So, I have no idea how
> common it is to use nested classes in this manner, but I expect that someone
> has found it useful at some point.
> 
> I thought that this meaning of static for nested classes came from Java, but
> it's been a while since I've done much with Java, so I don't know.

Yeah, it's very similar in D and Java.

Another example that comes from Java (before version 8) is to have a 
class with a nested anonymous class that implements an interface. It's 
very common in Java for event handling or similar actions. Other 
languages like D or Java 8 would use a delegate/lambda for the same 
thing. Something like:

class WindowController
{
     Button button;
     Window window;

     this()
     {
         button = new Button;
         window = new Window;
         button.onClick = new class() Clickable {
             window.close();
         };
     }
}

The anonymous class could have been a named class as well and to be able 
to access the "window" instance variable of the controller it needs to 
have access to the outer context and cannot be static.

-- 
/Jacob Carlborg


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