Re: Warning on self assignment
On Wednesday, April 25, 2018 02:32:32 Per Nordlöw via Digitalmars-d-learn wrote: > On Wednesday, 25 April 2018 at 02:23:04 UTC, Mike Franklin wrote: > > Are people using self assignment of structs as a way of > > force-running the postblit? Is there a valid use case for that? > > > > Mike > > If they are, there should be a better way of force-running the > postblit. Under what circumstances would it be reasonable to force the postblit to run? Certainly, under any kind of normal circumstances, the postblit constructor should only be run as a result of the object being copied - which the compiler controls. - Jonathan M Davis
Re: Warning on self assignment
On Wednesday, 25 April 2018 at 03:32:09 UTC, Meta wrote: On Wednesday, 25 April 2018 at 02:32:32 UTC, Per Nordlöw wrote: On Wednesday, 25 April 2018 at 02:23:04 UTC, Mike Franklin wrote: Are people using self assignment of structs as a way of force-running the postblit? Is there a valid use case for that? Mike If they are, there should be a better way of force-running the postblit. You can call __postblit or __xpostblit (I think the latter is a postblit introduced via a mixin or template mixin). Thanks
Re: Warning on self assignment
On Wednesday, April 25, 2018 02:23:04 Mike Franklin via Digitalmars-d-learn
wrote:
> On Wednesday, 25 April 2018 at 01:08:46 UTC, Arun Chandrasekaran
>
> wrote:
> > So I was telling my colleague that D would warn on self
> > assignment, but found that I was wrong.
> >
> > https://run.dlang.io/is/HLhtek
> >
> > ```
> > module a;
> >
> > import std.stdio;
> >
> > void main() {
> >
> > string a;
> > a = a; // Can the compiler warn at this line that
> >
> > there is no effect?
> >
> > writeln(a);
> > return;
> >
> > }
> > ```
>
> Are people using self assignment of structs as a way of
> force-running the postblit? Is there a valid use case for that?
I would be _very_ surprised if there were a valid reason to do that. That
being said, it's not necessarily true that
a = a;
has no effect. In the case of string that's basically true, but if the type
has a postblit constructor, then it definitely can have an effect (e.g. it
allocates memory or prints out that the object was copied). I don't think
that it's at all likely to have a desirable effect, and I would expect for
it to be fine for
a = a;
to be deprecated and then turned into an error on the grounds that there
isn't a reasonable reason to do it and is probably a bug - especially in
cases such as
this(A a, B b)
{
a = a;
b = b;
}
but it's likely untrue in the general case to say that that statement has no
effect.
- Jonathan M Davis
Re: Warning on self assignment
On Wednesday, April 25, 2018 03:32:09 Meta via Digitalmars-d-learn wrote: > On Wednesday, 25 April 2018 at 02:32:32 UTC, Per Nordlöw wrote: > > On Wednesday, 25 April 2018 at 02:23:04 UTC, Mike Franklin > > > > wrote: > >> Are people using self assignment of structs as a way of > >> force-running the postblit? Is there a valid use case for > >> that? > >> > >> Mike > > > > If they are, there should be a better way of force-running the > > postblit. > > You can call __postblit or __xpostblit (I think the latter is a > postblit introduced via a mixin or template mixin). I seriously question that it's ever a good idea to call either, but __postblit is the actual postblit constructor declared in the struct, and __xpostblit is the function that deals with calling the postblit constructor on all of the member variables and then calling __postblit. - Jonathan M Davis
Re: Warning on self assignment
On Wednesday, 25 April 2018 at 01:20:13 UTC, Mike Franklin wrote: It appears a bug has already been filed (https://issues.dlang.org/show_bug.cgi?id=11970). I'll see if I can fix it. https://github.com/dlang/dmd/pull/8208 We'll see what happens.
Re: Warning on self assignment
On Wednesday, 25 April 2018 at 02:32:32 UTC, Per Nordlöw wrote: On Wednesday, 25 April 2018 at 02:23:04 UTC, Mike Franklin wrote: Are people using self assignment of structs as a way of force-running the postblit? Is there a valid use case for that? Mike If they are, there should be a better way of force-running the postblit. You can call __postblit or __xpostblit (I think the latter is a postblit introduced via a mixin or template mixin).
Re: Warning on self assignment
On Wednesday, 25 April 2018 at 02:23:04 UTC, Mike Franklin wrote: Are people using self assignment of structs as a way of force-running the postblit? Is there a valid use case for that? Mike If they are, there should be a better way of force-running the postblit.
Re: Warning on self assignment
On Wednesday, 25 April 2018 at 01:08:46 UTC, Arun Chandrasekaran
wrote:
So I was telling my colleague that D would warn on self
assignment, but found that I was wrong.
https://run.dlang.io/is/HLhtek
```
module a;
import std.stdio;
void main() {
string a;
a = a; // Can the compiler warn at this line that
there is no effect?
writeln(a);
return;
}
```
Are people using self assignment of structs as a way of
force-running the postblit? Is there a valid use case for that?
Mike
Re: Warning on self assignment
On Wednesday, 25 April 2018 at 01:08:46 UTC, Arun Chandrasekaran
wrote:
So I was telling my colleague that D would warn on self
assignment, but found that I was wrong.
https://run.dlang.io/is/HLhtek
```
module a;
import std.stdio;
void main() {
string a;
a = a; // Can the compiler warn at this line that
there is no effect?
writeln(a);
return;
}
```
It appears a bug has already been filed
(https://issues.dlang.org/show_bug.cgi?id=11970). I'll see if I
can fix it.
Mike
Warning on self assignment
So I was telling my colleague that D would warn on self
assignment, but found that I was wrong.
https://run.dlang.io/is/HLhtek
```
module a;
import std.stdio;
void main() {
string a;
a = a; // Can the compiler warn at this line that
there is no effect?
writeln(a);
return;
}
```
