Hi,

This week, following the discussions on the PR for lowering _d_arrayappend{cTX,T} to templates, my mentors and I decided we should probably change the implementation of the template hooks themselves.

Because of the fact that _d_arrayappendT only appends 2 arrays, if the rhs is a single element, the lowering of lhs ~= rhs currently has to look like this:

_d_arrayappendcTX(lhs, 1), a[lhs.length - 1] = rhs, lhs;

This makes it impossible for CTFE to convert the lowering back to lhs ~= rhs. Therefore, the complete lowering is:

__ctfe ? lhs ~= rhs : _d_arrayappendcTX(lhs, 1), a[lhs.length - 1] = rhs, lhs;

This lowering is problematic because the IR generator has to discard the CondExp and its true branch manually.

We asked this question on the forum about the issue above. In it, we propose to extend _d_arrayappendT to be able to concatenate both arrays and single elements to the lhs array, so that semantic3 can simply lower the lhs ~= rhs to _d_arrayappendT every time.

Additionally, I started working on the _d_newitem{U,iT,T} hooks. It is likely we won't be able to remove the usage of TypeInfo from _d_newitemU. The old hook writes the TypeInfo object at the end of the newly created struct object. This is most likely in order to help the GC. We asked yet another question on the forum about this TypeInfo object and whether its removal would cause trouble or not.

Thanks,
Teodor