They are supposed to match C. But they don't for unary operators + - ~, and as far as I can tell never did.

  https://issues.dlang.org/show_bug.cgi?id=16997
  https://issues.dlang.org/show_bug.cgi?id=17637

Note that the spec says:

"Note: unlike in C and C++, the usual integral promotions are not performed prior to the complement operation."

  http://dlang.org/spec/expression.html#complement_expressions

Where did that come from?

And the spec says nothing about unary - or unary +.

  http://dlang.org/spec/expression.html#unary-expression

It's been like this at least since D1, both the code and the Spec.

So, we have a choice:

1. Fix it so it matches C, as has been generally promised. Fixing it will break existing code such as:

  https://github.com/dlang/phobos/pull/5646

but worse, it may silently break code. I don't know of a reasonable way to detect this.

2. Codify existing practice, since it has been that way forever. Not matching C has caused problems, see 16997 and 17637. It may cause more serious silent problems for people converting C code to D code.

Walter Bright wrote:

> 2. Codify existing practice, since it has been that way forever. Not matching C has caused problems, see 16997 and 17637. It may cause more serious silent problems for people converting C code to D code.

i'd say "codify, and add warning". since i patched the warning into the compiler, i have no more problems with the current rules: compiler tells me about possible incompatibilities with C, and i can either add `()` to silent the warning, or explicitly cast to the type i want.

i think most other people will prefer to get warning instead of code breakage too. at least i hope so. ;-)

This affects:

~ubyte: all values
-ubyte: all values
-byte: -128 (0x80)

~ushort: all values
-ushort: all values
-short: -32768 (0x8000)

On Saturday, 22 July 2017 at 10:51:05 UTC, ketmar wrote:
> Walter Bright wrote:
>
>> 2. Codify existing practice, since it has been that way forever. Not matching C has caused problems, see 16997 and 17637. It may cause more serious silent problems for people converting C code to D code.
>
> i'd say "codify, and add warning".

I'd vote for the ketmar solution if workable.

Another argument for this is that C code that has already been converted to D, and is currently silently broken, would benefit from a new warning as a way of gathering attention. However matching C promotion might make this code work too but silently.

On Saturday, 22 July 2017 at 10:44:04 UTC, Walter Bright wrote:
> Note that the spec says:
>
> "Note: unlike in C and C++, the usual integral promotions are not performed prior to the complement operation."
>
>   http://dlang.org/spec/expression.html#complement_expressions
>
> Where did that come from?

Git blames you:

https://github.com/dlang/dlang.org/commit/4cd3f38bbabdde30b280738dab4f4184c06f05f9

On Saturday, 22 July 2017 at 10:51:05 UTC, ketmar wrote:
> Walter Bright wrote:
>
>> 2. Codify existing practice, since it has been that way forever. Not matching C has caused problems, see 16997 and 17637. It may cause more serious silent problems for people converting C code to D code.
>
> i'd say "codify, and add warning". since i patched the warning into the compiler, i have no more problems with the current rules: compiler tells me about possible incompatibilities with C, and i can either add `()` to silent the warning, or explicitly cast to the type i want.
>
> i think most other people will prefer to get warning instead of code breakage too. at least i hope so. ;-)

Good luck adding a warning into DMD. After years there still isn't a warning for unsigned/signed comparisons.

What code would break? Are there any examples of D code that would break as a result of the change?

Jerry wrote:

> What code would break? Are there any examples of D code that would break as a result of the change?

basically, any template that has small integral type T and does unary +/-/~ on it. and there *is* such code in phobos, and it's not explicitly tested for different integral sizes. when i added a warning, i had to fix phobos in several places, but i'm pretty sure that there are ALOT more.

On 7/22/2017 1:07 PM, Vladimir Panteleev wrote:
> Git blames you:
> 
> https://github.com/dlang/dlang.org/commit/4cd3f38bbabdde30b280738dab4f4184c06f05f9

Ah, thanks for finding this. It was in response to:

  https://issues.dlang.org/show_bug.cgi?id=5132

i.e. it was documenting existing behavior.

OT: https://issues.dlang.org/show_bug.cgi?id=17417 can we also reconsider this?

On 7/24/2017 1:50 AM, Kagamin wrote:
> OT: https://issues.dlang.org/show_bug.cgi?id=17417 can we also reconsider this?

The bugzilla page was pretty clear about it.