Compile time executable calling?

[Walter Bright]

On 7/12/2013 1:42 PM, Tofu Ninja wrote:
> So I had an idea recently, wouldn't it be cool to have the ability to call an
> executable at compile time and capture its output. Something like the string
> imports but instead of opening and reading a text file, it run an executable,
> waits for it to finish, and grabs its output.
>
> It would get really cool if you could pass this executable some args and then
> mix in its out put into your own code. It could be used similarly to how CTFE
> are used but with out the overhead of trying to compile that function and what
> not and with out the limitations on what it can do.
>
> I could imagine all sorts of things that would be possible with this that is
> currently not.
>
> Not sure if this is something that could be implemented easily, but seems like
> something that could be done and something that would be really cool.

This is actually done in the makefile that builds DMD. A program (optabgen) is 
compiled and then run. Optabgen's output is several .c files which are then 
compiled into DMD's binary. The programs impcnvgen and idgen do similar things.

It is a very powerful technique.