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.
