nested functions and closures

[Johannes Pfau]

Am Mon, 11 Feb 2013 17:03:22 -0500
schrieb "Steven Schveighoffer" <schveiguy at yahoo.com>:

> 
> A nested class has an outer pointer to it's owner class.  You cannot  
> instantiate a nested class without it's owner class.
> 
> A nested struct does NOT have a pointer to it's owner class.  It's
> simply typed inside the class' namespace.
> 
> FYI, nested classes were enshrined with a pointer to an outer
> instance for two reasons:
> 
> 1. Their footprint is larger, not as big a hit to add another pointer.
> 2. To allow porting of Java code.
> 
> Structs are POD for the most part, and are much more "bare metal"
> than classes.
> 
> Nested structs could be given an instance pointer to the owner, but
> I think we would need a new construct for that.

Thanks, I thought it was something like that. The weird part is that if
you return a nested struct which is nested in a _function_ the compiler
generates a closure for the function and then struct is given an
instance pointer to the closure. But if you return a struct nested in a
class the struct doesn't get an instance pointer.

> For your problem at hand, you may want to consider using interfaces  
> instead.  Or you can possibly embed the owner pointer manually.
> 
> -Steve

Fortunately there's no problem at hand, I was just curious :-) I
actually use nested classes/structs and closures quite rarely.