On 12/10/12 1:55 PM, Jacob Carlborg wrote:
On 2012-12-10 17:06, Dan wrote:
I think so. Here is a claim I think is true: gdup must do full deep copy
to be safe and guarantee the transitive const/immutable. If it is
implemented such that there are no casts, then the compiler does its job
and ensures everything is good. If there are casts they need to be
deemed safe - I have one cast to work around issues in associative array
iteration.
I'm pretty sure it can't be done.
Just like Dan I thought it can be done but actually ownership is
impossible to establish in general. Consider:
class List(T) {
List next;
T payload;
...
}
versus
class Window {
Window parent;
...
}
It's pretty obvious from the name that duplicating a List would entail
duplicating its tail, whereas duplicating a Window would entail just
copying the reference to the same parent. However, at the type level
there's no distinction between the two members.
Now, user-defined attributes could change the playfield radically here.
Consider we define things like @owned and @foreign that would inform the
gdup or deepdup function appropriately:
class List(T) {
@owned List next;
T payload;
...
}
versus
class Window {
@foreign Window parent;
...
}
Now a generic deep duplication function has enough information to
duplicate things appropriately.
Andrei
