On 6/20/16 10:45 PM, Joerg Joergonson wrote:
On Monday, 20 June 2016 at 23:35:28 UTC, Steven Schveighoffer wrote:
On 6/19/16 5:19 PM, Joerg Joergonson wrote:
On Sunday, 19 June 2016 at 20:21:35 UTC, ag0aep6g wrote:
On 06/19/2016 09:59 PM, Joerg Joergonson wrote:
This should be completely valid since B!T' obviously derives from A!T
directly
ok
and we see that T' derives from b which derives from a
directly.
ok
So B!b is an entirely derived from A!a
No. B!b is derived from A!b, not from A!a. `b` being derived from `a`
does not make A!b derived from A!a.
why not? This doesn't seem logical!
Because:
class A(T : a)
{
static if(is(T == a))
int oops;
...
}
Now A!b and A!a have different layouts. They cannot be related, even
if the template arguments are related. I could introduce another
virtual function inside the static if, same result -- vtable is messed
up.
In general, an instantiation of a template aggregate (class or struct)
is not castable implicitly to another instantiation of the same
aggregate unless explicitly declared.
And note that D does not allow multiple inheritance. I don't think you
can solve this problem in D.
Yes, but all you guys are doing is leaving out what I'm actually doing
and creating a different problem that may not have the same issues.
We're not "creating" any different problems. The compiler has to assume
the worst, especially when it must make assumptions at runtime. The same
template instantiated with different parameters is different, not
related. In order for it to be related, you have to declare that somehow.
-Steve
