On Monday, 10 December 2012 at 20:10:25 UTC, Andrei Alexandrescu
wrote:
You want to create a new window with the same parent. At the
top level there's one desktop window, and probably having two
would be odd.
Ok - so I'm only talking about structs.
What you say is what you want here and it makes sense. But that
is not what I'm proposing. I'm just talking deep copy of structs
that is always deep copy - period (bearophile called it
transitive copy). By design that means there is no aliasing at
all. So in this case the parent window would be deep copied. This
can be done without any change to the struct (cycles when
pointers are used are one design issue that would need to be
addressed). This is also why gdup can be used to copy any
immutable(T) into T (assuming is(T==struct)) and get around the
"how do I copy const/immutable instances" we see so often.
Below illustrates what would happen and you would not want it for
Window parent/child relationships - but you see the consistency.
For what you describe you want reference semantics and gdup is
not needed.
Given this - I think the original claim still holds.
I claim that gidup or igdup or whatever
can just be:
@property auto gidup(T)(const ref T t) {
immutable(T) result = cast(immutable)(t.gdup);
return result;
}
I am not saying you can or should gdup any struct instance willy
nilly, just that the cast to immutable here is safe because all
fields are deep copied recursively.
------------------- output -------
Window("c1", 5, 5, 7FFF5BF3F4F0)
Window("c1", 5, 5, 7FAC74004FE0)
-------------------
import std.stdio;
import opmix.mix;
struct Window {
string name;
int x, y;
Window *parent;
}
void main() {
auto window = Window("root", 1, 1);
auto child = Window("c1", 5, 5, &window);
auto c2 = child.gdup;
writeln(child);
writeln(c2);
}
