Hi,

This week I implemented a template version of _d_newThrowable and I'm currently working on moving the lowering to it from e2ir.d to expressionsem.d. This requires a call to _d_newThrowable, as well as setting vthis and vthis2, if the exception's class is nested, and then calling its ctor. I'm still working on the latter steps of the lowering.

At the same time, I started looking at _d_arraycatnTX, starting from Dan Printzell's work:

• https://github.com/dlang/dmd/pull/10064
• https://github.com/dlang/druntime/pull/2648/

However, Dan's templated hook is actually just a wrapper that calls the old hook. This makes both the hook itself and the lowering difficult to maintain and inefficient, because of the 2D-array that's created by the compiler before being linearised. Thus, after I've decided to reimplement _d_arraycatnTX to use variadic templates instead of the 2D-array trick. This will make the implementation much cleaner in both the compiler and in DRruntime. I'm currently stuck on the _d_arraycatnTXTrace alias, however. As it's currently implemented, the hook for traceGC doesn't seem to be instantiable with a variadic template Tarr. I'm still exploring solutions for this problem, but I might have to implement the hook myself, without relying on HookTraceImpl.

Happy New Year!

Thanks,
Teodor