Adding empty static this() causes exception

[Moritz Maxeiner via Digitalmars-d-learn]

On Tuesday, 12 September 2017 at 09:11:20 UTC, Joseph wrote:
> I have two nearly duplicate files I added a static this() to 
> initialize some static members of an interface.
>
> On one file when I add an empty static this() it crashes while 
> the other one does not.
>
> The exception that happens is
> Cyclic dependency between module A and B.
>
> Why does this occur on an empty static this? Is it being ran 
> twice or something? Anyway to fix this?

The compiler errors because the spec states [1]

>> Each module is assumed to depend on any imported modules being 
>> statically constructed first

, which means two modules that import each other and both use 
static construction have no valid static construction order.

One reason, I think, why the spec states that is because in 
theory it would not always be possible for the compiler to decide 
the order, e.g. when executing them changes the ("shared") 
execution environment's state:

---
module a;
import b;

static this()
{
     // Does something to the OS state
     syscall_a();
}
---

---
module b;
import a;

static this()
{
     // Also does something to the OS state
     syscall_b();
}
---

The "fix" as I see it would be to either not use static 
construction in modules that import each other, or propose a set 
of rules for the spec that define a always solvable subset for 
the compiler.

[1] https://dlang.org/spec/module.html#order_of_static_ctor