[duelingjello]

In a C compiler (cc command), there are only compilation units (.c -> .o). Headers (.h) were bolted-on (cpp command) to deduplicate interfaces (forward declarations).

This header-only containing implementations adds its code to every compilation unit and the linker has to be smart enough to deduplicate identical symbols across many compilation units. Linkers (ld command) are provided either by the platform vendor or the compiler vendor, so they may or may not be able to do this. Binutils on Linux is able to do so IIRC.

It's a terrible practice that promotes cowboy coding. It should just use two files, which would cause less problems in the real world.

You can also write C without headers or newlines. IOCCC may welcome it but why would you ship it or encourage people to use it?

[cellularmitosis]

> This header-only containing implementations adds its code to every compilation unit and the linker has to be smart enough to deduplicate identical symbols across many compilation units.

That's not how this works. It's actually a pretty clever trick, and it effectively behaves as a .h / .c pair of files. See https://github.com/nothings/stb/blob/master/docs/stb_howto.t...

[ninkendo]

“Clever trick” should be treated as a pejorative.

Knowing why I have to `#define FOO_IMPL` before I include the header, but only from one of my compilation units, is a “clever trick” that now anybody reading or maintaining my code has to tuck away into their brain as well. Along with all the other tricks they’ve had to memorize because some other asshole thought they were being clever too.