On Mon, 16 Nov 2009 17:01:32 +0300, dsimcha <dsim...@yahoo.com> wrote:
== Quote from Walter Bright (newshou...@digitalmars.com)'s article
Denis Koroskin wrote:
> C standard library alloca function has an undefined behavior when
> requested size is large enough to cause a stack overflow, but many
> (good) implementations return null instead. So does DMD, for example.
I
> believe it would be even better to go ahead and enforce D
implementation
> to return a GC allocated chunk of memory instead of null in that case.
> It will not incur any performance hit in 99.9% of the cases and
prevent
> a bug from being happen in the rest. It will also make writing code
> using it easier (and more safe), since you don't have to worry about
> possible stack overflow/null-dereference.
I'm a little reluctant to do this because alloca is supposed to be a low
level routine, not one that has a dependency on the rather large and
complex gc. A person using alloca is expecting stack allocation, and
that it goes away after the function exits. Switching arbitrarily to the
gc will not be detected and may hide a programming error (asking for a
gigantic piece of memory is not anticipated for alloca, and could be
caused by an overflow or logic error in calculating its size).
And secondly, I wish to emphasize that a null pointer seg fault is not
an unsafe thing. It does not lead to memory corruption. It simply stops
the program.
Yes, but it stops the program in such a way that it's very hard to
figure out
why/where it died. The solution, which I've wanted for a while and I
think others
have proposed, is for DMD to implicitly assert that every pointer is
non-null
before dereferencing it when in debug mode.
... or use the type system to enforce all/most of the pointers to be
non-null.
