On Thu, 31 Jan 2013 10:12:53 -0500, Andrei Alexandrescu
<seewebsiteforem...@erdani.org> wrote:
On 1/31/13 10:03 AM, Steven Schveighoffer wrote:
On Thu, 31 Jan 2013 07:27:08 -0500, d coder <dlang.co...@gmail.com>
wrote:
On Thu, Jan 31, 2013 at 5:30 PM, monarch_dodra
<monarchdo...@gmail.com> wrote:
The pull is kind of stuck in limbo, specifically because of the
problems
associated with implementing reference semantics with structs :/
Thanks for the enlightening email.
I am of the considered view that reference semantics with structs in D
is tough (if not impossible) with default constructor and postblit
constructor (used when passing objects). This is because you can not
initialize any object (wrapped in the struct) in the default
constructor and if you are passing the struct as a function parameter,
it is not possible to initialize these internal objects (before
passing them) in the postblit constructor. I faced this in some of my
code. Do not know if you are facing the same scenario in the DList
implementation.
It's pretty simple. Containers are reference types, and it makes most
sense to pass them by reference.
In order to be sane, containers must be implemented as classes.
Otherwise, you have behavior like this:
void foo(int[int] aa, int x, int y)
{
aa[x] = y;
}
void main()
{
int[int] aa;
foo(aa, 1, 2);
aa[3] = 4;
foo(aa, 5, 6);
assert(!(1 in aa));
assert(aa[3] == 4);
assert(aa[5] == 6);
}
In other words, the only way to turn a default-instantiated struct into
a valid struct is to use it once. Not the behavior you want.
Classes don't have this problem, because you must instantiate them to
use them.
As far as I can tell classes have the same problem.
Nope.
void foo(someclass aa, int x, int y)
{
aa[x] = y;
}
void main()
{
someclass aa;
foo(aa, 1, 2); // segfault
...
}
-Steve
