Header-Only Library - pragma(root)

[Adam D. Ruppe]

On Sunday, 14 June 2020 at 16:05:39 UTC, Andrei Alexandrescu 
wrote:
> What code wouldn't it work with?

It isn't so much code as it is some build paradigms.

If you are forced to do separate compilation (like if dmd is 
eating 30 GB of RAM...), you can't enjoy dmd -i just working. But 
you can still use it in individual pieces then link the result 
together normally, so it doesn't get in your way, it just doesn't 
help as much. If you do it wrong in these cases, you are liable 
to get duplicate symbol problems with a diamond dependency (two 
packages compiled separately that both include a common third 
package).

All manageable and -i can still help in these cases with 
appropriate inclusion/exclusion patterns, just -i's biggest 
strength is when you are doing an all-at-once build.

Ditto with non-module based dependency versions or compilation 
flags, since those again bring you back to separate compilation.

The other semi-tricky thing is dub's default source layout 
doesn't follow the convention -i expects due to having the extra 
source/ directory. So you need to add it with -Iproject/source 
each time. Or you can automatically rearrange files from a 
package upon downloading it (just read the `module` declaration 
and sort it into directories from that under a common `lib` 
top-level thing. This is actually what I do on my computer and 
why my arsd repo has most its files at top-level - if you clone 
the repo in your lib dir, the files are now right at `arsd/cgi.d` 
etc... which automatically works with the compiler. Zero extra 
config needed, it all just works. I get a lot of complaints about 
that layout but this is an objective advantage I don't think a 
lot of people really realize!)


I've been tempted before to write a competing package manager 
that does stuff like this all automatically. Imagine you just 
write some D and `import foo.bar;` then the compiler (or, more 
specifically, the helper program that works with the compiler) 
tells you "module foo.bar is not installed but can be found in 
package `footech`, install now? (y/n)". And if you made the major 
version part of the module names instead of git tags, that'd all 
magically just work too. I'd be kinda fun and very efficient 
thanks to dmd -i.