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digitalmars.D.learn - Are static variables available to other static variables?

reply Jamie <notme gmail.com> writes:
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
}
Apr 12 2019
next sibling parent Dennis <dkorpel gmail.com> writes:
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.
Apr 12 2019
prev sibling parent reply Jamie <notme gmail.com> writes:
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;
     }
}
Apr 12 2019
next sibling parent Simen =?UTF-8?B?S2rDpnLDpXM=?= <simen.kjaras gmail.com> writes:
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
Apr 12 2019
prev sibling next sibling parent XavierAP <n3minis-git yahoo.es> writes:
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. 

initializations at run-time during the first use of C.
Apr 12 2019
prev sibling parent XavierAP <n3minis-git yahoo.es> writes:
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"
Apr 12 2019