On 07/13/2010 01:59 PM, Vladimir Panteleev wrote:
On Tue, 13 Jul 2010 21:36:02 +0300, Andrei Alexandrescu
<seewebsiteforem...@erdani.org> wrote:
Not quite. New is different because it is a primitive - it can't be
implemented as a function (well it could if it user placement new, but
we're back to square one). In contrast, delete already knows the type
of the object it's destroying and can call the destructor manually so
it is easy to implement as a regular function.
Sorry, not following you here. Why can't new be implemented as a
templated function which takes the type of the object to create as a
template parameter? Isn't it just allocation, copying over T.init, then
calling the constructor with whatever arguments the user passed?
In D it's possible to call the constructor by issuing __ctor(). In C++
there is no way, hence the presence of a language primitive.
But manual deletion has no business in the garbage collected heap.
Isn't that making the assumption that all D programs are garbage-collected?
No. It is not making that assumption.
That currently druntime provides it is an accident caused by
thecurrent implementation; most GC's cannot provide efficient manual
reclamation. And they shouldn't anyway.
Why not? And what if I don't use the GC (just the
allocation/deallocation aspects of it)?
You should use malloc() and free() for manual memory management and the
GC for automatic memory management. Each of these two is ill-suited for
carrying the other's job.
(There's a longer discussion underneath this concerning what memory
really is and what GCs really are and do.)
I understand your points regarding leaving deallocation to happen on a
GC run being more efficient than manually deallocating objects
individually,
I didn't make that point.
but this doesn't cover all use-cases. Also, what if I need
to deallocate a large block of memory right now? I'd be forced to use
the more verbose and less safe "free" functions.
To manually manage a large memory block, you may want to use malloc()
and free(). Again: manual free() should NOT be counted on in a garbage
collector.
Andrei
