On Tuesday, 17 July 2012 at 23:38:04 UTC, Jonathan M Davis wrote:
It's not that it makes the compiler's life hard. It's the fact
that
conditional compilation relies on state that doesn't exist yet.
It's messed up
to be checking whether an object defines something when you're
in the middle of
defining that object.
[snip]
- Jonathan M Davis
Well, while you "can" do it in C++ as the "Curiously Recursive
Template Pattern" (particularly popular way of implementing the
singleton pattern BTW), you can't just do anything you feel like
doing with it.
If I remember correctly, in C++, you can't access any of T's
members, or create any (stack) instances of T, or (I think) call
T's any of T's static members, because "T is not correctly formed
yet".
Did you try anything more advanced? For example, this outright
_crashes_ my (r)dmd:
--------
class MyBase(T)
{
int a = T.hello();
}
class MySubA : MyBase!MySubA
{
static int hello(){return 0;}
}
--------
I'm not entirely sure how valid the comparison with C++'s CRTP
is, because D's classes are actually pointer to implementation,
but I think it is a safe bet that what C++ can't do, neither can
D.
