Writing/Creating files at compile-time

[JDemler via Digitalmars-d]

On Sunday, 9 August 2015 at 14:00:55 UTC, Rikki Cattermole wrote:
> On 10/08/2015 1:57 a.m., cym13 wrote:
>> On Sunday, 9 August 2015 at 13:51:21 UTC, Andrei Alexandrescu 
>> wrote:
>>> On 8/9/15 5:07 AM, JDemler wrote:
>>>> We can read files at compile-time:
>>>>
>>>>    enum file = import(fileName);
>>>>
>>>> But we cannot write to a file or create files at compile 
>>>> time.
>>>>
>>>> Generating code at compile-time and mixing it in is fun but 
>>>> has a few
>>>> flaws.
>>>> It isn't debuggable, the generated code cannot be directly 
>>>> inspected (we
>>>> have to use pragma(msg, )) and it is not possible to 
>>>> manually tweak it.
>>>>
>>>> If we could generate source files (.d) at compile time and 
>>>> then import
>>>> them using mixins or something else, these problems can be 
>>>> dealt with.
>>>
>>> I think this is an interesting pursuit that closes the circle 
>>> on a
>>> number of issues, such as debuggability and compilation speed 
>>> of mixin
>>> code. -- Andrei
>>
>> The moment this is added to D, we will have two complete 
>> languages in
>> one: an interpreted one at compile-time and another at runtime.
>>
>> While I find this interesting, I wonder wether this is  a good 
>> idea or not.
>
> I'm actually at the point where I believe the addition of 
> string import was a bad one. No. I prefer preprocessing into a 
> D file first.
> It irks me, you have to be pretty careful with them, but at 
> least a preprocessed file you know _exactly_ where all files 
> need to be for CT.

Consider vibe.d's diet templates: They are compiled into d code 
using information of the types provided by the user.
Without string imports at compile-time that would either result 
in a two-step compile process or would rely on run-time type 
information. Both is nothing I would like to use.

Imagine the .dt files could be compiled into .dt.d files and then 
imported at compile-time. The development process would be much 
easier (debugging and examining the source files becomes trivial) 
and the usage would be more transparent (I see what my .dt file 
gets compiled into) and would have faster compile times (as 
Andrei mentioned).