Launch and obtain thread output during compile time

[data pulverizer via Digitalmars-d-learn]

On Sunday, 13 August 2017 at 08:09:28 UTC, Petar Kirov 
[ZombineDev] wrote:
> On Sunday, 13 August 2017 at 07:37:15 UTC, data pulverizer 
> wrote:
>> Hi all,
>>
>> Is it possible to launch/spawn a thread/fibre or some other 
>> appropriate item and obtain an immutable/enum or some 
>> appropriate output at compile-time? For instance return an 
>> immutable(string) from the external thread to be used as the 
>> input to a template parameter or a CTFE function. To be clear 
>> the thread carries out run-time processing e.g. reading a file.
>>
>> Thanks in advance.
>
> No, CTFE is single-threaded and additionally it is required 
> that functions executed at compile-time are "pure", i.e. they 
> don't affect the global state of the system and don't use any 
> non-portable facilities. Essentially, only pure computation is 
> allowed.
>
> Though, specifically reading files is allowed at compile-time 
> via the `string s = import("file.txt");` syntax, provided that 
> the file `file.txt` is located in a directory, specified to the 
> compiler by the `-J` flag. For more information see:
> http://dlang.org/spec/expression.html#import_expressions

Thank you. Great explanation!