Should this be possible? I admit to not being fully clear on the way delegates are handled, but maybe someone can shed some light? As an example I use a snippet Ali uses to demonstrate opApply:

struct NumberRange {
  int begin;
  int end;

  int opApply(int delegate(ref int) @nogc operations) @nogc const {
    int result = 0;

    for (int number = begin; number != end; ++number) {
      result = operations(number);

      if (result) {
        break;
      }
    }
    return result;
  }
}

void main() {
  import std.stdio;
  foreach (element; NumberRange(3, 7)) { // line 21
    write(element, ' ');
  }
}

When I compile this with 2.066.0 I get

opapply.d(21): Error: function opapply.NumberRange.opApply (int delegate(ref int) @nogc operations) const is not callable using argument types (int delegate(ref int __applyArg0) @system)

It doesn't actually complain about anything gc, just about the signature, so I was wondering if there is some restriction inside the foreach implementation that can be lifted? Thanks in advance for any hints!

On Sun, 24 Aug 2014 13:22:49 +0000
Stefan Frijters via Digitalmars-d-learn
<digitalmars-d-learn@puremagic.com> wrote:

@nogc is a part of signature. gc-function can't call @nogc-one. the same is with calling @system function from @safe one, for example. or impure function from pure.

so to say, foreach() creates implicit delegate withoit '@nogc' attribute, that's why compiler complains.

there is currenly no way to specify attributes for such implicit delegates. this will work, but you'll not be able to call writeln():

  nogc:
  void main() {
     import std.stdio;
     foreach (element; NumberRange(3, 7)) { // line 21
       //write(element, ' '); // this will fail with
         // @nogc function 'z00.main.__foreachbody1' cannot call
         // non-@nogc function 'std.stdio.write!(int, char).write'
    }
  }

what we need here is something like:

  foreach (element; NumberRange(3, 7) @nogc) { ... }

but alas...

ketmar:

> there is currenly no way to specify attributes for such implicit
> delegates.

It could be a nice language enhancement.

Bye,
bearophile

On Sun, 24 Aug 2014 13:58:45 +0000
bearophile via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com>
wrote:

> > there is currenly no way to specify attributes for such implicit delegates.
> It could be a nice language enhancement.
i agree. but i tend not to fill enhancement requests without corresponding patches, and i'm not yet familiar with D frontend enough to create the patch.

ketmar:

> but i tend not to fill enhancement requests without
> corresponding patches,

I agree that having a patch ready is much better. But people like me file hundreds of ERs without too much damage done, and many of them get eventually implemented. If you find a D limitation, then putting this information in Bugzilla is better than letting this get forgotten.

Bye,
bearophile

On Sun, 24 Aug 2014 14:34:02 +0000
bearophile via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com>
wrote:

> putting this information in Bugzilla is better than letting this get forgotten.
so it can be forgotten in Bugzilla. ;-)

ketmar:

> so it can be forgotten in Bugzilla. ;-)

And in ten, or one hundred or one thousand years the whole D language will be forgotten. There are various levels of remembering and forgetting. Putting bugs and ERs in databases is a different kind of forgetting.

Bye,
bearophile

On Sun, Aug 24, 2014 at 05:49:29PM +0300, ketmar via Digitalmars-d-learn wrote:
> On Sun, 24 Aug 2014 14:34:02 +0000
> bearophile via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com>
> wrote:
> 
> > putting this information in Bugzilla is better than letting this get forgotten.
> so it can be forgotten in Bugzilla. ;-)

Some of us regularly comb through old bugzilla issues to find things to test & fix. It may take a long time, but we do try. :-)

(And we could use a lot of help -- there are only a few of us and a ton
of old bugs.)


T

-- 
Perhaps the most widespread illusion is that if we were in power we would behave very differently from those who now hold it---when, in truth, in order to get power we would have to become very much like them. -- Unknown

On Sun, 24 Aug 2014 08:02:40 -0700
"H. S. Teoh via Digitalmars-d-learn"
<digitalmars-d-learn@puremagic.com> wrote:

> Some of us regularly comb through old bugzilla issues to find things to test & fix. It may take a long time, but we do try. :-)
> 
> (And we could use a lot of help -- there are only a few of us and a
> ton of old bugs.)
i understand that. it was a joke, i'm not trying to being rude or ranting about some of my "pet bugs". ;-)

On Sunday, 24 August 2014 at 14:34:03 UTC, bearophile wrote:
> ketmar:
>
>> but i tend not to fill enhancement requests without
>> corresponding patches,
>
> I agree that having a patch ready is much better. But people like me file hundreds of ERs without too much damage done, and many of them get eventually implemented. If you find a D limitation, then putting this information in Bugzilla is better than letting this get forgotten.
>
> Bye,
> bearophile

I would also prefer to submit a patch but I do not have the skills to do it at the moment, so I filed an enhancement request: https://issues.dlang.org/show_bug.cgi?id=13370 .