On Sunday, 23 January 2022 at 15:35:17 UTC, Paul Backus wrote:
The main benefit of having multiple versions available in separate namespaces is that it allows them to coexist in the same project, which means that users can migrate their code incrementally from one to the other.
Yeah, I know the theory, but in practice this has limited value and works best for more fine-grained things (e.g. keeping deprecated individual functions around are more helpful than whole modules).
The bigger the thing, the more likely that you'll actually introduce more bugs and compatibility issues trying to keep both versions working anyway.
In principle you could also accomplish this with a versioned dub package and mangle-prefix [1], but progress on that initiative seems to have stalled out.
Well, that's because it was a hopeless idea from the beginning. The in-language `import` doesn't know anything about mangles, so this concept was just asking for trouble. It would work if any only if the dependencies were *completely* isolated, but even something as simple as you importing library A who uses v1.struct at the same time as library B who uses v2.struct - even if lib A and lib B's usage of that struct was entirely `private` - is liable to cause ABI crashes. Something like PIMPL can still make it work, but there's no guarantee they did that, and likely no expectation that they would in typical D code.
Anyone who has debugged extern(C) crashes after a library update knows these situations are not fun.
