In what order static if conditions are evaluated?

[deadalnix]

On Thursday, 28 March 2013 at 11:52:26 UTC, Don wrote:
> On Thursday, 28 March 2013 at 11:29:49 UTC, Artur Zawłocki 
> wrote:
>> Hi,
>>
>> DMD (I'm using v2.060) seems to evaluate conditions in static 
>> if's from top to bottom (at least in a given scope). For 
>> example, consider the following program:
>>
>>  module test;
>>
>>  const bool x = true;
>>  const bool y = true;
>>
>>  struct S {
>>
>>    static assert(y);
>>
>>    static if(x)
>>       static const bool y = false;
>>
>>    static if(y)
>>       static const bool x = false;
>>  }
>>
>> 'x' in the first static if condition refers to .x and the 
>> static if introduces S.y to which 'y' in the second static if 
>> refers. 'y' in the static assert also refers to S.y and thus 
>> the assertion fails:
>>
>>  test.d(8): Error: static assert  (y) is false
>>
>> Now, I guess if the second static if were evaluated first then 
>> 'y' in the static assert condition would refer to .y and the 
>> program would compile. Note that dmd evaluates the static 
>> assert *after* both static if's.
>>
>> So clearly D program semantics depends on the order static 
>> if's and static assert's are evaluated. Are there any standard 
>> rules here (I cannot find anything in Language Reference) or 
>> is this behaviour implementation dependent?
>>
>> Artur
>
> Yes, it currently evaluates it top to bottom. An algorithm has 
> been discussed which would remove that restriction; your 
> example would then compile. It's difficult to implement though. 
> It has to deal with paradoxes:
>
> static if (!is(typeof(x)) int y = 1;
> static if (!is(typeof(y)) int x = 1;
>
> Who wins?

Current already have to deal with paradoxes.