// ------ Example: ----------

template A(alias Arg) {
	enum A = Arg;
	enum Unrelated = ({return 0;})(); // this line prevent compilation
};

void main() {
	enum FnPtr = &asdf;
	enum _ = A!FnPtr;
};

void asdf() {};

// ( https://dpaste.dzfl.pl/79301f12e5fc )

Just by having a random `({return 0;})()` in the template body, suddenly the template rejects its arguments. I'm so confused, is this a bug? Or am I missing something?

On Wednesday, 17 August 2016 at 13:09:40 UTC, Cauterite wrote:
> Just by having a random `({return 0;})()` in the template body, suddenly the template rejects its arguments. I'm so confused, is this a bug? Or am I missing something?

Function pointers and delegates are not valid compile time variables.

Best you can do is use them in an alias argument directly, but you cannot use them in an enum argument.

On Wednesday, 17 August 2016 at 13:18:06 UTC, Adam D. Ruppe wrote:
> Best you can do is use them in an alias argument directly, but you cannot use them in an enum argument.

I think you missed the point; it works perfectly fine without having this `({return 0;})()` in the template body (which, as far as I can see, doesn't appear to interact at all with the template argument).

On Wednesday, 17 August 2016 at 13:21:16 UTC, Cauterite wrote:
> On Wednesday, 17 August 2016 at 13:18:06 UTC, Adam D. Ruppe wrote:
>> Best you can do is use them in an alias argument directly, but you cannot use them in an enum argument.
>
> I think you missed the point; it works perfectly fine without having this `({return 0;})()` in the template body (which, as far as I can see, doesn't appear to interact at all with the template argument).

I think he meant that  ({ return 0;})() cannot be executed at compile time and assigned to an enum. That's why the instantiation is failing.

On 8/17/16 9:23 AM, Lodovico Giaretta wrote:
> On Wednesday, 17 August 2016 at 13:21:16 UTC, Cauterite wrote:
>> On Wednesday, 17 August 2016 at 13:18:06 UTC, Adam D. Ruppe wrote:
>>> Best you can do is use them in an alias argument directly, but you
>>> cannot use them in an enum argument.
>>
>> I think you missed the point; it works perfectly fine without having
>> this `({return 0;})()` in the template body (which, as far as I can
>> see, doesn't appear to interact at all with the template argument).
>
> I think he meant that  ({ return 0;})() cannot be executed at compile
> time and assigned to an enum. That's why the instantiation is failing.

Yes, it can: https://dpaste.dzfl.pl/fca15065a4cf

I think the OP's case is a bug. Please file.

-Steve

On Wednesday, 17 August 2016 at 13:33:26 UTC, Steven Schveighoffer wrote:
> I think the OP's case is a bug. Please file.

Thanks, I've filed it. Just wanted to get a second opinion before concluding that it's a bug.