It seems to me that this is what linkers and static/dynamic libs are for. Why does it also then have to exist in the compiler? I suppose there's the problem of

It seems to me that this is what linkers and static/dynamic libs are for. Why does it also then have to exist in the compiler? I suppose there's the problem of optimization across module boundaries, but if you solve that problem for compilers, might as well solve it for linkers. What you're describing sounds like my current best practice for developing iOS apps. I have multiple static libraries for separate logical code units that don't have to be recompiled when unrelated code is changed. This is for C, C++, ObjC and Swift. All iOS package managers have the option to download compiled binaries, as well.