On 07/18/2012 11:08 PM, monarch_dodra wrote:
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;}
}
--------
Well, that is a bug.
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.
Careful there. D allows forward references. This is all supposed to work
in D. (but DMD is poor when it comes to tricky symbol lookup tasks.)
