Re: static weirdness
On 1/25/18 8:24 AM, Mike Parker wrote: On Thursday, 25 January 2018 at 12:58:12 UTC, Jonathan M Davis wrote: Thinking about it, I do vaguely recall a discussion sometime last year about an invariant being invisibly inserted under some set of circumstances. Maybe that's what's happening? I believe that it was complained about in that discussion, so maybe it was removed after that. Certainly, if I try that code locally with master, it runs just fine without hitting any assertions. https://dlang.org/changelog/2.077.0.html#removePreludeAssert I think that changelog is wrong. The prelude assert was added I think to all member calls. And it has been removed. -Steve
Re: static weirdness
On Thursday, 25 January 2018 at 12:58:12 UTC, Jonathan M Davis wrote: Thinking about it, I do vaguely recall a discussion sometime last year about an invariant being invisibly inserted under some set of circumstances. Maybe that's what's happening? I believe that it was complained about in that discussion, so maybe it was removed after that. Certainly, if I try that code locally with master, it runs just fine without hitting any assertions. https://dlang.org/changelog/2.077.0.html#removePreludeAssert
Re: static weirdness
On Thursday, January 25, 2018 12:42:57 Kagamin via Digitalmars-d-learn wrote: > See https://ideone.com/VZ97dh I don't know what's going on there. Such an assertion does not seem in line with what Walter has typically said on the subject. Thinking about it, I do vaguely recall a discussion sometime last year about an invariant being invisibly inserted under some set of circumstances. Maybe that's what's happening? I believe that it was complained about in that discussion, so maybe it was removed after that. Certainly, if I try that code locally with master, it runs just fine without hitting any assertions. - Jonathan M Davis
Re: static weirdness
See https://ideone.com/VZ97dh
Re: static weirdness
On Thursday, January 25, 2018 12:38:25 Kagamin via Digitalmars-d-learn
wrote:
> On Thursday, 25 January 2018 at 12:06:07 UTC, Jonathan M Davis
>
> wrote:
> > Actually, assert on a pointer to a struct or a reference to a
> > class checks for null _and_ calls the invariant, and that
> > hasn't changed. But you have to actually assert the pointer or
> > reference if you want to do that, and the OP didn't do that. He
> > asserted whether it == null.
>
> I mean the compiler implicitly inserted a check like:
> struct S
> {
> auto fun()
> {
> assert(!=null);
> return 42;
> }
> }
AFAIK, it has never done that. Walter's stance on null pointers has always
been that that's what segfaults are for, and he's against adding any
additional null checks.
- Jonathan M Davis
Re: static weirdness
On Thursday, 25 January 2018 at 12:06:07 UTC, Jonathan M Davis
wrote:
Actually, assert on a pointer to a struct or a reference to a
class checks for null _and_ calls the invariant, and that
hasn't changed. But you have to actually assert the pointer or
reference if you want to do that, and the OP didn't do that. He
asserted whether it == null.
I mean the compiler implicitly inserted a check like:
struct S
{
auto fun()
{
assert(!=null);
return 42;
}
}
Re: static weirdness
On Thursday, 25 January 2018 at 12:06:07 UTC, Jonathan M Davis wrote: On Thursday, January 25, 2018 10:17:34 Kagamin via Digitalmars-d-learn wrote: On Wednesday, 24 January 2018 at 02:01:54 UTC, Jonathan M Davis wrote: > (so there's no need to dereference the pointer to call it) It used to check this pointer with an assert. When did it change? Actually, assert on a pointer to a struct or a reference to a class checks for null _and_ calls the invariant, and that hasn't changed. But you have to actually assert the pointer or reference if you want to do that, and the OP didn't do that. He asserted whether it == null. - Jonathan M Davis Yeah... the cool thing is, that if the function does not need anything from the referenced object, then the pointer "degenerates" to a "namespace" implicitly... sorry, for strange wording. It seems that this behavior changed from 2.076.1 to 2.077.
Re: static weirdness
On Thursday, 25 January 2018 at 10:17:34 UTC, Kagamin wrote: On Wednesday, 24 January 2018 at 02:01:54 UTC, Jonathan M Davis wrote: (so there's no need to dereference the pointer to call it) It used to check this pointer with an assert. When did it change? Fortunately, I have some compilers here and just tested it. 2.076.1 results in a segmentation fault, whereas 2.077.0 does not.
Re: static weirdness
On Thursday, January 25, 2018 10:17:34 Kagamin via Digitalmars-d-learn wrote: > On Wednesday, 24 January 2018 at 02:01:54 UTC, Jonathan M Davis > > wrote: > > (so there's no need to dereference the pointer to call it) > > It used to check this pointer with an assert. When did it change? Actually, assert on a pointer to a struct or a reference to a class checks for null _and_ calls the invariant, and that hasn't changed. But you have to actually assert the pointer or reference if you want to do that, and the OP didn't do that. He asserted whether it == null. - Jonathan M Davis
Re: static weirdness
On Wednesday, 24 January 2018 at 02:01:54 UTC, Jonathan M Davis wrote: (so there's no need to dereference the pointer to call it) It used to check this pointer with an assert. When did it change?
Re: static weirdness
On Wednesday, 24 January 2018 at 02:01:54 UTC, Jonathan M Davis
wrote:
On Wednesday, January 24, 2018 01:48:45 Alex via
Digitalmars-d-learn wrote:
the story of
https://forum.dlang.org/thread/qknxjxzbaowmsjdng...@forum.dlang.org continues
How can this be?
void main()
{
auto s = S();
auto t = T!s();
assert(typeof(t).dummy == null);
assert(t.dummy == null);
t.foo;
}
struct S
{
auto fun()
{
return 42;
}
}
struct T(alias stats)
{
static typeof(stats)* dummy; // line 21
static auto foo()
{
assert(dummy == null); // line 24
assert(dummy.fun == 42); //line 25
}
}
I thought, if I don't initialize a pointer, like the one in
line
21 (I assert this by the check in line 24) I can't use it line
line 25.
However, I can...
That has nothing to do with static. That has to do with the
fact that S.fun
is non-virtual (so there's no need to dereference the pointer
to call it),
and fun doesn't access any members, so it doesn't need to
dereference the
this pointer internally either. And since the pointer is never
dereferenced,
it doesn't matter that it's null.
That's cool, by the way :)
You'd get the same behavior if you used
a non-static S.
On a side note, if you're checking for null, it's better to use
the is operator rather than ==. For strings, there's a semantic
difference, so it really matters. For classes, it avoids
calling the free function opEquals (which will give the same
result, but it's a pointless function call when you could just
use is and avoid the call). For pointers, it matters that much
less, but since it does matter in the other cases (especially
strings), it's a good habit to get into just using is null
instead of == null.
Thanks.
Re: static weirdness
On Wednesday, January 24, 2018 01:48:45 Alex via Digitalmars-d-learn wrote:
> the story of
> https://forum.dlang.org/thread/qknxjxzbaowmsjdng...@forum.dlang.org
> continues
>
> How can this be?
>
> void main()
> {
> auto s = S();
> auto t = T!s();
> assert(typeof(t).dummy == null);
> assert(t.dummy == null);
> t.foo;
>
> }
>
> struct S
> {
> auto fun()
> {
> return 42;
> }
> }
>
> struct T(alias stats)
> {
> static typeof(stats)* dummy; // line 21
> static auto foo()
> {
> assert(dummy == null); // line 24
> assert(dummy.fun == 42); //line 25
> }
> }
>
> I thought, if I don't initialize a pointer, like the one in line
> 21 (I assert this by the check in line 24) I can't use it line
> line 25.
> However, I can...
That has nothing to do with static. That has to do with the fact that S.fun
is non-virtual (so there's no need to dereference the pointer to call it),
and fun doesn't access any members, so it doesn't need to dereference the
this pointer internally either. And since the pointer is never dereferenced,
it doesn't matter that it's null. You'd get the same behavior if you used
a non-static S.
On a side note, if you're checking for null, it's better to use the is
operator rather than ==. For strings, there's a semantic difference, so it
really matters. For classes, it avoids calling the free function opEquals
(which will give the same result, but it's a pointless function call when
you could just use is and avoid the call). For pointers, it matters that
much less, but since it does matter in the other cases (especially strings),
it's a good habit to get into just using is null instead of == null.
- Jonathan M Davis
Re: static weirdness
On Wednesday, 24 January 2018 at 01:48:45 UTC, Alex wrote: Ah... I figured it out. For using the function of S, an object does not have to exist... And in case I would return a member from S, there is a segmentation violation, as expected. So, everything is ok. Sorry for noise.
static weirdness
the story of
https://forum.dlang.org/thread/qknxjxzbaowmsjdng...@forum.dlang.org
continues
How can this be?
void main()
{
auto s = S();
auto t = T!s();
assert(typeof(t).dummy == null);
assert(t.dummy == null);
t.foo;
}
struct S
{
auto fun()
{
return 42;
}
}
struct T(alias stats)
{
static typeof(stats)* dummy; // line 21
static auto foo()
{
assert(dummy == null); // line 24
assert(dummy.fun == 42); //line 25
}
}
I thought, if I don't initialize a pointer, like the one in line
21 (I assert this by the check in line 24) I can't use it line
line 25.
However, I can...
