Re: The case for transpiled generics

On Thu, 17 Sep 2020 at 20:25, Levi Morrison via internals < internals@lists.php.net> wrote: > > In summary: > - Checked at run-time (and probably also compile-time when possible): > reified generics. > - Checked only at compile-time and thrown away at run-time: erased > generics. > - Not checked at all: ____?. Maybe we can call them "ignored generics"? > I think this is making the common assumption that "official" static analysis and compilation are necessarily the same process, but the compiler itself only needs to "understand" enough to choose a target representation; running other analysis at the same time is just a choice for programmer convenience. My understanding is that in reality there are three stages: 1) Static analysis: checks may be made whether erasing or reifying, because erasure hasn't happened yet. 2) Compilation: erased generics are converted to non-generic types; reified generics are compiled to a representation available at run-time 3) Run-time: reified generics have run-time behaviour; erased generics aren't ignored, they simply don't exist because the compiler already erased them In PHP, we currently have a compile step, run on-demand, but do not have an official static analysis step. I have said before that in order to make the type system richer without sacrificing run-time performance, we need to consider having such an official tool. That could be run automatically alongside the existing on-demand compilation; it could be entirely manual as a separate tool; or it could be combined with a new, manually executed compiler or transpiler. I believe there is precedent for all of these approaches. Regards, -- Rowan Tommins [IMSoP]