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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