I'm not sure this opt-in/out "philosophical razor" is as sharp as one would like it to be. I think "optionality" alone oversimplifies and a person trying to adopt that rule for taxonomy would just have a really hard time and that might be telling us something.
For example, in Nim, at the compiler CLI tool level, there is opt-in/opt-out via the `--mm=whatever` flag, but, at the syntax level, Nim has both `ref T` and `ptr T` on equal syntactic footing . But then in the stdlib, `ref` types (really things derived from `seq[T]`) are used much more (since it's so convenient). Meanwhile, runtimes are often deployment properties. If every Linux distro had their libc link against -lgc for Boehm, people might say "C is a GC'd language on Linux". Minimal CRTs vary across userspaces and OS kernel/userspace deployment.. "What you can rely on/assume", I suspect the thrust behind "optionality", just varies with context.
Similar binding vagueness between properties (good, bad, ugly) of a language's '"main" compiler' and a 'language itself' and 'its "std"lib' and "common" runtimes/usage happen all the time (e.g. "object-oriented", often diluted by the vagueness of "oriented"). That doesn't even bring in "use by common dependencies" which is an almost independent axis/dimension and starts to relate to coordination problems of "What should even be in a 'std'-lib or any lib, anyway?".
I suspect this rule is trying to make the adjective "GC'd" do more work in an absolute sense than it realistically can given the diversity of PLangs (sometimes not so visible considering only workaday corporate PLangs). It's not always easy to define things!
> I think "optionality" alone oversimplifies and a person trying to adopt that rule for taxonomy would just have a really hard time and that might be telling us something.
I think optionality is what gives that definition weight.
Think of it this way. You come to a project like a game engine, but you find it's written in some language and discover for your usage you need no/minimal GC. How hard is it to minimize or remove GC. Assume that changing build flags will also cause problems elsewhere due to behavior change.
> Similar binding vagueness between properties (good, bad, ugly) of a language's '"main" compiler' and a 'language itself' and 'its "std"lib' and "common" runtimes/usage happen all the time (e.g. "object-oriented", often diluted by the vagueness of "oriented")
Vagueness is the intrinsic quality of human language. You can't escape it.
The logic is fuzzy, but going around saying stuff like "Rust is a GC language" because it has an optional, rarely used Arc/Rc, is just off the charts level of wrong.
