Conpile-Time module constructor

[Paul Backus]

On Sunday, 19 June 2022 at 15:57:41 UTC, Ruby The Roobster wrote:
> On 6/19/2022 11:55 AM, Paul Backus wrote:
>> 
>> 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.

You're right--technically, it doesn't check whether the module is 
*included* in the final build, only whether the module is 
*available* for inclusion at compile time.

Because D supports separate compilation of modules, there is no 
way to check at compile time what modules will be included in the 
final build. If that's what you want to test for, you will have 
to move the check out of the code itself and into your build 
system (for example, by passing a `-version=HasMyModule` flag for 
builds that include the module in question).