> Is a translation unit the same as in C, but since you're #including the file you would expect multiple compilations of a re-included C file? woudnt this bloat the resulting executable (/ bundle in case of a library)
I think the idea is that compiling a translation unit produces two outputs, the object code (as it currently does), and an intermediate representation of the exported declarations, that could be basically a generated .h file, but it would probably be more efficient to use a different format. Then dependent translation units use those declaration files.
With this, you can still compile in parallel. You are constrained by the order of dependencies, but that is already kind of the case.
One complication is that ideally, if the signature doesn't change, but the implementation does, you don't need to re-compile dependent translation units. This is trivial if your build system detects changes based on content (like, say, bazel), but if it uses timestamps (like make) then the compiler needs to ensure the timestamp isn't updated when the declarations don't change.
But this really isn't a new concept. Basically every modern compiled language works fine without needing separate header files.
> This is trivial if your build system detects changes based on content (like, say, bazel), but if it uses timestamps (like make) then the compiler needs to ensure the timestamp isn't updated when the declarations don't change.
This is where the traditional distinction of "compiler vs Make" makes things harder; you want dependencies tracked at the "declaration" level, rather than the file level. If the timestamp _and_ content of the exported declarations file change, but none of the _used_ declarations changed, then there's no more compilation to be done. At best with file level tracking your build system will invoke the compiler for every downstream dependency, and they can decide if there's any more work to be done.
The build system would need to know which declarations are used (and what a declaration is) to do better.
The D compiler has an option to generate a "header file" from D modules. It's called a .di file. It's useful if you want to hide the implementation from a compiler, as you would with libraries.
As it turned out, though, people just found it too convenient to just import the .d file.
But as a very unexpected dividend, it was discovered that the D compiler would generate .di files from compiling .c files, and realized that D had an inherent ability to translate C code to D code!!!! This has become rather popular.
I think the idea is that compiling a translation unit produces two outputs, the object code (as it currently does), and an intermediate representation of the exported declarations, that could be basically a generated .h file, but it would probably be more efficient to use a different format. Then dependent translation units use those declaration files.
With this, you can still compile in parallel. You are constrained by the order of dependencies, but that is already kind of the case.
One complication is that ideally, if the signature doesn't change, but the implementation does, you don't need to re-compile dependent translation units. This is trivial if your build system detects changes based on content (like, say, bazel), but if it uses timestamps (like make) then the compiler needs to ensure the timestamp isn't updated when the declarations don't change.
But this really isn't a new concept. Basically every modern compiled language works fine without needing separate header files.