Struct no-arg constructor?

[deadalnix]

Le 25/07/2012 12:30, monarch_dodra a écrit :
> On Wednesday, 25 July 2012 at 09:51:49 UTC, Jonathan M Davis wrote:
>> If you want to be able to do S(), then declare a static opCall for S
>> which
>> returns an S constructed in the way that you want.
>>
>> struct S
>> {
>> static S opCall()
>> {
>> //do whatever you do
>> return s;
>> }
>> }
>>
>> auto s = S();
>>
>> but
>>
>> S s;
>>
>> will always be init. But you can't have a default constructor, because
>> then it
>> conflicts with what init would be doing. e.g. would
>>
>> S s;
>> [SNIP]
>
> This makes *so* much sense now. I couldn't understand the point of "S a
> = S();" up until now. Thanks a lot.
>
> I read TDPL back to back like 5 times before posting this, but it never
> mentions opCall. I just checked the index right now, it is not in there.
> Is this new?
>
> Provided the existence of "opCall", though why would I keep writing
> constructors?
>

new S(args); // Allocate on the heap instead of the stack

But forget about new S();

> Also, while I understand why we can't have a "default" constructor, your
> explanations perfectly proves we *can* have a "no-arg" (subtle
> difference) one:
> S s = S(); //Initialize s to this();
> S s; //Leave s as S.init
>
> It seems like opCall is a bypass to a language restriction...

It is. If something should go, it is for me the static opCall hack.