static assert(0) in template is a disaster

[Avrina]

On Wednesday, 17 June 2020 at 01:34:18 UTC, Stefan Koch wrote:
> On Wednesday, 17 June 2020 at 01:26:48 UTC, Andrei Alexandrescu 
> wrote:
>> On 6/16/20 7:01 PM, Paul Backus wrote:
>>> I agree that this is a bug, but it is a bug in the design of 
>>> the language itself, not the implementation.
>>
>> Is that a sort of a compile-time race condition? If that's the 
>> case, D should deem the program ill-formed with no diagnostic 
>> required.
>
> That is ......
> I lack the words.
> I must be misunderstanding.
>
> Are you saying that it is fine for D to act differently on code 
> that used to compile fine,
> because we don't want to detect order-dependency issues?
>
> Please clearify.

It's more than a order-dependency issue.

   pragma(msg, Foo.tupleof.length); // prints 1

   struct Foo {
  	int a;

     static if(Foo.tupleof.length == 1) {
     	int b;
     }
     static if(Foo.tupleof.length == 2) {
     	int c;
     }
   }

   pragma(msg, Foo.tupleof.length); // prints 1

   void main() {
     writeln(Foo.tupleof.length); // prints 2
   }



If you try to do the same thing with "Foo.sizeof == 4/8" in the 
`static if`'s you get a compile error. Some attempt was made to 
prevent this situation, but not much. It doesn't make sense to 
probe information that isn't known at the time, or cannot be 
known at any time in that scope. It is ill-formed.