12-Sep-2014 16:43, Atila Neves пишет:
I know about the differences between C++ const and D const. I'm not
talking about head-const, tail-const or logical const.
If I'm not mistaken, the last thing that happened to me was storing the
captures from a regex into a const variable, then I couldn't index it.
I didn't look at the implementation, but it's very weird to me that
getting an element can't be done on a const object. And yes, I'll look
into doing a PR for it.
My problem with const is that people try to use it as often as logical
const in C++ (everywhere), it DOESN'T HAVE to be as used as often.
Being binary-wise immutable is harsh requirement on implementation, and
forbids many techniques (like COW and ref-counting). That's one reason
we might never have const Captures in std.regex.
I'm using stdx.data.json a bit now as well, and will have to give
feedback there. I can't make anything const, it seems.
I wasn't aware of @safe stdio, it always annoyed me that @safe functions
can't call writeln, that never made any sense to me.
Atila
On Friday, 12 September 2014 at 10:19:27 UTC, Jakob Ovrum wrote:
On Friday, 12 September 2014 at 09:53:45 UTC, Atila Neves wrote:
This happens to me all the time. I write a function, stick the
aforementioned attributes on as a default then let the compiler tell
me when I can't.
That happens a lot more often than I thought it would. Pretty much
anytime I call a Phobos function I have to remove at least one of
them but usually all three.
Is it similar for everyone else? Is it considered a problem?
Phobos still hasn't been fully annotated since these attributes were
introduced, but we are making progress. For one, I believe we got
@safe std.stdio recently, which should be a big boost for @safe
adoption in general.
It is slowly getting better. Pull requests are welcome.
The other thing is I frequently have to "unconstify" my variables to
get them accepted by Phobos functions as well.
D's const is very different from C++'s const. It's tempting to use in
the same situations because of superficial similarities, but D's const
should only be used when immutable is in the picture. D simply doesn't
have the equivalent of C++'s const (which is intentional), despite
their similar names.
That said, there are fundamental issues with const and immutable that
have yet to be resolved - for example, given an immutable container or
a const reference to a container, it's not possible to get a
head-mutable range over it for iteration. This is different from
in-built slices which are conveniently convertible from const(T[]) to
const(T)[], something that is not expressible with user-defined types
at the moment.
Further, `inout` does not support considering callback parameters to
be "out parameters":
struct S
{
int* p;
inout(int)* foo() inout { return p; } // OK
void bar(void delegate(inout int*) dg) inout { // Not supported
dg(p);
}
}
Both of these issues have been discussed before and IIRC, consensus
seemed to be that we do want to do something about them.
--
Dmitry Olshansky
