On Sunday, 29 April 2012 at 17:29:03 UTC, Simen Kjaeraas wrote:
On Sun, 29 Apr 2012 14:28:05 +0200, Namespace
<rswhi...@googlemail.com> wrote:
On Sunday, 29 April 2012 at 11:24:00 UTC, Simen Kjaeraas wrote:
On Sun, 29 Apr 2012 10:14:09 +0200, Namespace
<rswhi...@googlemail.com> wrote:
Based on my previous thread
(http://forum.dlang.org/thread/rpcqefmyqigftxsgs...@forum.dlang.org),
I got the question whether it is possible to restrict "alias
this"?
Similar to templates function, e.g. "void foo(T)(T value) if
(isNumeric!(T) ...", but it should be limited here so that
it does not interact with the cast or something other.
As far as I know, "alias this" is an implicit cast. And just
like an explicit cast (opCast) it should be possible to
restrict it.
Otherwise, I have unfortunately run out of ideas how I can
allow an implicit conversion.
What do you mean restrict it?
I mean that you can limit it similar as you can with
templates. In my code i'm using "alias this" to enable an
implicit conversion from any class, e.g. Foo, to Ref!Foo. Ref
is an struct which checks if the value of Foo is null. If it's
null a error message will let you know, that you have a
problem with one of your objects (i hate the access violation
message, that's the original reason for that).
But if i cast with a class, that implements the implicit
conversion, as in the following:
[code]
class A {
mixin TRef!(A);
}
class B : A { }
A a1 = new B();
B b1 = cast(B) a1.access; // <- problem
[/code]
the cast will implicit convert with "alias this" to Ref!B. And
that isn't what i want and neither what should happen. In this
case a limit to "alias this" would be great. A limitation,
that "alias this" must not convert the cast to Ref!B.
But that's not what happens. a1's compile-time type is A, so
the compiler looks
up 'access' in A, but finds nothing. So it tries the alias
this, gets a Ref!A,
and calls access on that. At this point, T is A, so access
returns an A.
Then, the compiler tries to convert that A to a B, and gets
confused. This is
absolutely a bug. In fact, it is the bug Jesse Phillips
reported[1].
[1]: http://d.puremagic.com/issues/show_bug.cgi?id=8001
Yes, I've just noticed that. Are there already workarounds for
that problem?
