How to get an inout constructor working with a template wrapper
Timoses
timosesu at gmail.com
Mon Jul 23 14:46:32 UTC 2018
On Monday, 23 July 2018 at 12:02:58 UTC, aliak wrote:
>
> Thank you Ali! That helped :) I've gotten most of it sorted out
> now, and the factory wrap is definitely the way to go, it also
> turned out that inout(T) and inout T (so inout without parens)
> was surprisingly different (maybe it's a bug? - to test you can
> remove the parens around U on line 3 in this sample:
> https://run.dlang.io/is/gd5oxW
>
> Also over there, line 24:
>
> auto si = wrap!(immutable int)(3);
Both of these seem to work (as you pointed out)
// immutable(W!int)
auto si = wrap!(int)(cast(immutable)3); // or
wrap(cast(immutable)3);
// W!(immutable(int))
auto si2 = W!(immutable int)(3);
>
> seems to be giving problems. Any ideas there? Error is:
>
> onlineapp.d(8): Error: inout on return means inout must be on a
> parameter as well for pure nothrow @nogc @safe
> inout(W!(immutable(int)))(immutable(int) t)
> onlineapp.d(23): Error: template instance
> `onlineapp.wrap!(immutable(int))` error instantiating
>
> To make it compile successfully you can either:
>
> 1) Chance immutable to const, then it works for some reason.
> 2) Change the line to: "auto si = wrap(cast(immutable int)3);"
> - i.e. do not explicitly provide type information.
I don't know why
wrap!(immutable int)(3);
is not working. The error message
"Error: inout on return means inout must be on a parameter as
well for pure nothrow @nogc @safe
inout(W!(immutable(int)))(return immutable(int) t)"
sounds very odd and not at all helpful, at least regarding that
removing immutable from the template argument works.
>
> Cheers,
> - Ali
The depths of D. Why does the following only work with "return
ref"?
struct W(T) {
T val;
this(U : T)(auto ref inout U val) inout {
pragma(msg, typeof(val));
this.val = val;
}
}
// Fails without "return ref" (escaping t warning...)
auto wrap(T)(return ref inout T t) {
return inout W!T(t);
}
class C {}
void main() {
immutable C ci = new immutable C;
auto i = wrap(im);
pragma(msg, typeof(i));
}
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