It adds a ton to Clojure(script), including better error messages (yes!), data-structure shape declarations, generation of data, writing quickcheck (generative) tests for a function by just describing the args and return values of functions, and more.
It feels really uncomfortable declaring a full spec for a function & instrumenting it, then getting feedback if the args don't conform to spec but Clojure being A-OK if the return value doesn't.
I understand well that in theory the functioning of a function can be fully checked in a proactive test framework, but the process for testing return values is way clunkier and less fun than testing argument values. It just seems weird that the function has a spec, the function doesn't conform and Clojure doesn't seem to be bothered.
I can see it will only be a matter of days until I have Orchestra installed for all my projects.
I believe this is a missed opportunity to find bugs.
The things that are really the new big drivers are pieces that are not inside the language (other than a few spec integration points). Those things are significant pieces of work that are imminently usable now, but not quite final yet. In the interest of getting this work into more hands, we made a new release of the language with those parts marked as alpha.
The modularized spec allows us to continue releasing new versions (and for you to use them) with Clojure 1.9.0. Eventually spec will leave alpha and we will consider that a finalized part of the language. Similarly, tools.deps is still evolving as we work on it but the tools should remain fairly stable.
What are some good examples of this?
I would also love for it to apply to ClojureScript as well, although I understand that's a separate project.
The ClojureScript version of spec is largely API-compatible as well so the same specs should work in both.