On Saturday, 21 September 2013 at 11:35:11 UTC, bearophile wrote:
>
> init is part of a type and you can't change it.
>
> Bye,
> bearophile

Well, D wouldn't be D, if it did not allow something like this for aggregate types:

import core.stdc.string, std.stdio;

pure hack(T)(T value) if (is(T == class))
{
    byte[] init_mem = new byte[T.classinfo.init.length];
    memcpy(init_mem.ptr, cast(byte*)value, T.classinfo.init.length);
    T.classinfo.init = init_mem;
}

class A
{
   int a;
}

pure foo(int val)
{
   A a = new A;
   a.a++;
   hack(a);
   return a.a + val;
}

void main()
{
   writeln(0.foo, 0.foo, 0.foo); // prints 1,2,3
}

And taking into accout some additional runtime magic, assertion below may fail:

class A { int i = 5; }
struct S { A a;}
S s;
assert(s.a is null);

On Saturday, 21 September 2013 at 15:43:11 UTC, Maxim Fomin wrote:
> 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?

No, at compile-time. It's trivial to see if init is changed, but I want to see if it's set even if it's to T.init.

On Saturday, 21 September 2013 at 16:09:35 UTC, simendsjo wrote:
> On Saturday, 21 September 2013 at 15:43:11 UTC, Maxim Fomin wrote:
>> 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?
>
> No, at compile-time. It's trivial to see if init is changed, but I want to see if it's set even if it's to T.init.

I think there is a misunderstanding in your "a.init" and "b.init": This is just calling a static property on an instance. It's no different from T.init.

It *won't* tell you what a/b was initially initialized with.

If I understand correctly, you want:

int b = 3;
static assert(__traits(initialValue, b) == 3);

?

I don't think we have that. I'm not even sure we *can* have that.

On Saturday, 21 September 2013 at 16:09:35 UTC, simendsjo wrote:
> On Saturday, 21 September 2013 at 15:43:11 UTC, Maxim Fomin wrote:
>> 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?
>
> No, at compile-time. It's trivial to see if init is changed, but I want to see if it's set even if it's to T.init.

I see. No, I don't think this feature is suitable for declarative approach abuse ;)

Even if you manage to hack something, it is unlikely to be reliable, I'd recommend to stick to UDA's until compiler exposes that info.