I want to know if a variable has changed .init, but I don't know if it's possible if the .init value is the same. Does anyone have a solution for this?

    int a;
    int b = 0;
    pragma(msg, a.init); // 0
    pragma(msg, b.init); // 0
    // how can I see that b has "= 0"?

simendsjo:

> I want to know if a variable has changed .init, but I don't know if it's possible if the .init value is the same. Does anyone have a solution for this?
>
>     int a;
>     int b = 0;
>     pragma(msg, a.init); // 0
>     pragma(msg, b.init); // 0
>     // how can I see that b has "= 0"?

init is part of a type and you can't change it. a and by are both ints, and in both cases int.init is 0. I think there is no simple way to know if a variable has being default-initialized or not. Why do you want to know it?

Bye,
bearophile

On 9/21/13, bearophile <bearophileHUGS@lycos.com> wrote:
> I think there is no simple
> way to know if a variable has being default-initialized or not.
> Why do you want to know it?

There is however a way to extract it if it's a part of an aggregate:

-----
struct S
{
    int x = 1;
}

void main()
{
    static assert(S.x.init == 0);
    static assert(S.init.x == 1);
}
-----

On Saturday, 21 September 2013 at 12:50:20 UTC, Andrej Mitrovic wrote:
> On 9/21/13, bearophile <bearophileHUGS@lycos.com> wrote:
>> I think there is no simple
>> way to know if a variable has being default-initialized or not.
>> Why do you want to know it?
>
> There is however a way to extract it if it's a part of an aggregate:
>
> -----
> struct S
> {
>     int x = 1;
> }
>
> void main()
> {
>     static assert(S.x.init == 0);
>     static assert(S.init.x == 1);
> }
> -----

I'm though of using if for aggregates, yes. But this doesn't handle the case where you set the same value is T.init.

On Saturday, 21 September 2013 at 13:30:19 UTC, simendsjo wrote:
> I'm though of using if for aggregates, yes. But this doesn't handle the case where you set the same value is T.init.

I don't think those two case are any different from the type system point of view, manual or default.

On Saturday, 21 September 2013 at 13:38:44 UTC, Dicebot wrote:
> On Saturday, 21 September 2013 at 13:30:19 UTC, simendsjo wrote:
>> I'm though of using if for aggregates, yes. But this doesn't handle the case where you set the same value is T.init.
>
> I don't think those two case are any different from the type system point of view, manual or default.

Need some __traits(hasUserSuppliedInit, T) then :)

On Saturday, 21 September 2013 at 13:48:00 UTC, simendsjo wrote:
> On Saturday, 21 September 2013 at 13:38:44 UTC, Dicebot wrote:
>> On Saturday, 21 September 2013 at 13:30:19 UTC, simendsjo wrote:
>>> I'm though of using if for aggregates, yes. But this doesn't handle the case where you set the same value is T.init.
>>
>> I don't think those two case are any different from the type system point of view, manual or default.
>
> Need some __traits(hasUserSuppliedInit, T) then :)

I am not sure those differ even at compiler level (other than at syntax stage) - why would you need it?

On Saturday, 21 September 2013 at 13:55:00 UTC, Dicebot wrote:
> On Saturday, 21 September 2013 at 13:48:00 UTC, simendsjo wrote:
>> On Saturday, 21 September 2013 at 13:38:44 UTC, Dicebot wrote:
>>> On Saturday, 21 September 2013 at 13:30:19 UTC, simendsjo wrote:
>>>> I'm though of using if for aggregates, yes. But this doesn't handle the case where you set the same value is T.init.
>>>
>>> I don't think those two case are any different from the type system point of view, manual or default.
>>
>> Need some __traits(hasUserSuppliedInit, T) then :)
>
> I am not sure those differ even at compiler level (other than at syntax stage) - why would you need it?

I was thinking of "query by example". If a field has been set, it should be used in a where clause. But if I cannot see the difference between int.init and 0 for instance, it is impossible to get it right.
It's possible to solve this using UDAs of course.

On Saturday, 21 September 2013 at 14:11:44 UTC, simendsjo wrote:
> On Saturday, 21 September 2013 at 13:55:00 UTC, Dicebot wrote:
>> On Saturday, 21 September 2013 at 13:48:00 UTC, simendsjo wrote:
>>> On Saturday, 21 September 2013 at 13:38:44 UTC, Dicebot wrote:
>>>> On Saturday, 21 September 2013 at 13:30:19 UTC, simendsjo wrote:
>>>>> I'm though of using if for aggregates, yes. But this doesn't handle the case where you set the same value is T.init.
>>>>
>>>> I don't think those two case are any different from the type system point of view, manual or default.
>>>
>>> Need some __traits(hasUserSuppliedInit, T) then :)
>>
>> I am not sure those differ even at compiler level (other than at syntax stage) - why would you need it?
>
> I was thinking of "query by example". If a field has been set, it should be used in a where clause. But if I cannot see the difference between int.init and 0 for instance, it is impossible to get it right.
> It's possible to solve this using UDAs of course.

0 and int.init is the same. ;)

On Saturday, 21 September 2013 at 11:13:57 UTC, simendsjo wrote:
> I want to know if a variable has changed .init, but I don't know if it's possible if the .init value is the same. Does anyone have a solution for this?
>
>     int a;
>     int b = 0;
>     pragma(msg, a.init); // 0
>     pragma(msg, b.init); // 0
>     // how can I see that b has "= 0"?

Strictly speaking this is an ill-posed question. Are talking about testing at runtime whether some variable was changed from init to some non-default value?