Conpile-Time module constructor

[Ruby The Roobster]

On 6/19/2022 11:55 AM, Paul Backus wrote:
> On Sunday, 19 June 2022 at 15:34:48 UTC, Ruby The Roobster wrote:
>> On 6/19/2022 11:19 AM, Paul Backus wrote:
>>> On Sunday, 19 June 2022 at 14:51:26 UTC, Ruby The Roobster wrote:
>>>> Is it possible to make a module constructor run at compile-time?  If 
>>>> so, how?
>>>
>>> No, it's not.
>>>
>>> What are you trying to accomplish that lead you to ask this question? 
>>> There is probably a different way to do it without involving module 
>>> constructors.
>>
>> What I was trying to accomplish was to change a compile time array 
>> whenever a certain module was included.  The value of the array needs 
>> to be known at compile time.
> 
> You can do this with a `static if` check:
> 
>      static if (__traits(compiles, { import mymodule; }))
>      {
>          // mymodule is included
>          enum compileTimeArray = ...;
>      }

Curious - how exactly does this determine if the module is included?  I 
thought __traits(compiles, ...) only checks if an expression is 
SEMANTICALLY correct.