Implicit castable structs

[Kris]

Yeah, that's old-school inheritance. But I think it's probably a bit dodgy 
to sidestep type-safety to do what you want. Besides, it's not hard to write 
this instead (the old school way):

#  gtk_widget_foo (&bin->container.widget);

the codegen will be the same as just using 'bin' by itself, yet the 
type-safety is fully retained.

On the other hand, if there were an opCast() in the struct to support what 
you're suggesting ....

- Kris



"Frank Benoit" <keinfarbton at googlemail.com> wrote in message 
news:fm0vht$1tv7$1 at digitalmars.com...
> In GTK programming, there are struct that act like a object hierarchy.
>
> struct GtkWidget{ /* data member */ }
> struct GtkContainer{
> GtkWidget widget; // parent is always first member
> // more data members
> }
> struct GtkBin{
> GtkContainer container; // parent is always first member
> // more data members
> }
> extern(C) void gtk_widget_foo( GtkWidget* widget );
>
> // in user code ...
> GtkBin* bin;
> gtk_widget_foo( bin ); // Error: cannot implicit cast
>
> Can the D compiler be enhanced to allow this? More precisely:
> "A pointer to a struct is implicitly convertable to all types, that map to 
> the first position in the struct"
>
> In the case above, a GtkBin* would be convertable to GtkContainer* and 
> GtkWidget*. A GtkContainer* would /not/ be convertable to GtkBin* because 
> it does not contain it.
>