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Error with implicit cast of ^^=
Jul 13, 2021
wjoe
Jul 13, 2021
Ali Çehreli
Jul 14, 2021
wjoe
Jul 14, 2021
Ali Çehreli
Jul 15, 2021
wjoe
July 13, 2021
Gravatar of wjoePosted by wjoeReply
wjoe
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byte x = some_val;
long y = some_val;

x ^^= y; // Error:  cannot implicitly convert expression pow(cast(long)cast(int)x, y) of type long to byte

Is there a way to do this via ^^= ?

This is part of a unittest for opIndexOpAssign where the type of x is that of i.opIndex(_i). It's generated from a list of operators like this:

part_int_t!(1, 8, 10) i;
static assert(is(typeof(i[0]): short));
static assert(is(typeof(i[1]): byte));
static assert(is(typeof(i[2]): bool));
static foreach(op; ["+=", "-=", "^^=", ...])
{{
  typeof(i[1]) x;
  mixin("x" ~ op ~ "y;");
  mixin("i[1]" ~ op ~ "y;");
  assert(i == x);
}}

I rewrote it to something like

mixin("x = cast(typeof(x))(x" ~ op[0..$-1] ~ " y);");

but I'm curious if there's a less convoluted way.

July 13, 2021
Gravatar of Ali ÇehreliPosted by Ali Çehreli
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Ali Çehreli
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On 7/13/21 4:12 AM, wjoe wrote:
> ```D
> byte x = some_val;
> long y = some_val;
>
> x ^^= y; // Error:  cannot implicitly convert expression
> pow(cast(long)cast(int)x, y) of type long to byte

[...]

> I rewrote it to something like
> ```D
> mixin("x = cast(typeof(x))(x" ~ op[0..$-1] ~ " y);");
> ```
> but I'm curious if there's a less convoluted way.

If it's important, std.conv.to checks the value:

import std.conv;

void main() {
  byte x = 2;
  long y = 6;
  x = (x ^^ y).to!(typeof(x));
}

For example, run-time error if y == 7.

Ali
July 14, 2021
Gravatar of wjoePosted by wjoe
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wjoe
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On Tuesday, 13 July 2021 at 15:14:26 UTC, Ali Çehreli wrote:
> On 7/13/21 4:12 AM, wjoe wrote:
> > ```D
> > byte x = some_val;
> > long y = some_val;
> >
> > x ^^= y; // Error:  cannot implicitly convert expression
> > pow(cast(long)cast(int)x, y) of type long to byte
>
> [...]
>
> > I rewrote it to something like
> > ```D
> > mixin("x = cast(typeof(x))(x" ~ op[0..$-1] ~ " y);");
> > ```
> > but I'm curious if there's a less convoluted way.
>
> If it's important, std.conv.to checks the value:
>
> import std.conv;
>
> void main() {
>   byte x = 2;
>   long y = 6;
>   x = (x ^^ y).to!(typeof(x));
> }
>
> For example, run-time error if y == 7.
>
> Ali

I was planning on adding support for over-/underflow bits but this is much better. Thanks!
July 14, 2021
Gravatar of Ali ÇehreliPosted by Ali Çehreli
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Ali Çehreli
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On 7/14/21 2:44 AM, wjoe wrote:

>>   x = (x ^^ y).to!(typeof(x));
>> }
>>
>> For example, run-time error if y == 7.

> I was planning on adding support for over-/underflow bits but this is
> much better. Thanks!

If so, then there is also std.experimental.checkedint:

  https://dlang.org/phobos/std_experimental_checkedint.html

Andrei Alexandrescu introduced it in this presentation:

  https://dconf.org/2017/talks/alexandrescu.html

Ali
July 15, 2021
Gravatar of wjoePosted by wjoe
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wjoe
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On Wednesday, 14 July 2021 at 17:29:04 UTC, Ali Çehreli wrote:
> On 7/14/21 2:44 AM, wjoe wrote:
>
> >>   x = (x ^^ y).to!(typeof(x));
> >> }
> >>
> >> For example, run-time error if y == 7.
>
> > I was planning on adding support for over-/underflow bits but
> this is
> > much better. Thanks!
>
> If so, then there is also std.experimental.checkedint:
>
>   https://dlang.org/phobos/std_experimental_checkedint.html
>
> Andrei Alexandrescu introduced it in this presentation:
>
>   https://dconf.org/2017/talks/alexandrescu.html
>
> Ali

Thanks I'll have a look.