I was trying to declare a static variable dependent on another static variable, but it didn't work. Are static variables not known to other static variables at compile time?

void main()
{	
	C c = new C();
}

class C
{
    static size_t A = 2;
    static size_t B = 2^^A; // A is not known at compile time
}

On Friday, 12 April 2019 at 10:49:19 UTC, Jamie wrote:
> I was trying to declare a static variable dependent on another static variable, but it didn't work. Are static variables not known to other static variables at compile time?

Add `const` or `immutable` to A and it will work.
I don't know why B can't be initialized with A's initial value if A is mutable, but there's probably a rationale for that.

On Friday, 12 April 2019 at 10:49:19 UTC, Jamie wrote:
> I was trying to declare a static variable dependent on another static variable, but it didn't work. Are static variables not known to other static variables at compile time?
>
> void main()
> {	
> 	C c = new C();
> }
>
> class C
> {
>     static size_t A = 2;
>     static size_t B = 2^^A; // A is not known at compile time
> }

Ok I'm confused... why does that above not work but this does:

void main()
{	
    C c = new C();
}
class C
{
    static size_t A = 2;
    static size_t B;
    static this()
    {
        B = 2^^A;
    }
}

On Friday, 12 April 2019 at 10:56:32 UTC, Jamie wrote:
> On Friday, 12 April 2019 at 10:49:19 UTC, Jamie wrote:
>> I was trying to declare a static variable dependent on another static variable, but it didn't work. Are static variables not known to other static variables at compile time?
>>
>> void main()
>> {	
>> 	C c = new C();
>> }
>>
>> class C
>> {
>>     static size_t A = 2;
>>     static size_t B = 2^^A; // A is not known at compile time
>> }
>
> Ok I'm confused... why does that above not work but this does:
>
> void main()
> {	
>     C c = new C();
> }
> class C
> {
>     static size_t A = 2;
>     static size_t B;
>     static this()
>     {
>         B = 2^^A;
>     }
> }

A static constructor isn't run at compile time, but upon starting the program. Thus, values that are only available at run time can be used by a static constructor.

--
  Simen

On Friday, 12 April 2019 at 10:56:32 UTC, Jamie wrote:
> On Friday, 12 April 2019 at 10:49:19 UTC, Jamie wrote:
>> I was trying to declare a static variable dependent on another static variable, but it didn't work. Are static variables not known to other static variables at compile time?
>>
>> void main()
>> {	
>> 	C c = new C();
>> }
>>
>> class C
>> {
>>     static size_t A = 2;
>>     static size_t B = 2^^A; // A is not known at compile time
>> }
>
> Ok I'm confused... why does that above not work but this does:
>
> void main()
> {	
>     C c = new C();
> }
> class C
> {
>     static size_t A = 2;
>     static size_t B;
>     static this()
>     {
>         B = 2^^A;
>     }
> }

May this be a bug? Static mutable is a theoretically valid use case.

It looks to me that D often optimizes by evaluating at compile time. But in this case what is a possible optimization breaks a valid program when the optimization is found not to be possible. Other languages e.g. C# would by spec run these static initializations at run-time during the first use of C.

On Friday, 12 April 2019 at 10:56:32 UTC, Jamie wrote:
> On Friday, 12 April 2019 at 10:49:19 UTC, Jamie wrote:
>> I was trying to declare a static variable dependent on another static variable, but it didn't work. Are static variables not known to other static variables at compile time?
>>
>> void main()
>> {	
>> 	C c = new C();
>> }
>>
>> class C
>> {
>>     static size_t A = 2;
>>     static size_t B = 2^^A; // A is not known at compile time
>> }
>
> Ok I'm confused... why does that above not work but this does:
>
> void main()
> {	
>     C c = new C();
> }
> class C
> {
>     static size_t A = 2;
>     static size_t B;
>     static this()
>     {
>         B = 2^^A;
>     }
> }

It's not a bug. I finally found it in the spec:

https://dlang.org/spec/class.html#static-constructor

"All member initializations must be determinable by the compiler at compile time, hence there is no order-of-evaluation dependency for member initializations, and it is not possible to read a value that has not been initialized. Dynamic initialization is performed by a static constructor"