`in` parameters made useful

Fri Aug 21 09:37:37 UTC 2020

On Friday, 31 July 2020 at 21:49:25 UTC, Mathias LANG wrote:
> [...]

how does the ABI work for this for extern(C) and others? Will it 
mean ref or not ref / will that translate to a pointer or not?

For example in Win32 COM IDL files I often see [in] used for 
input only parameters, can we annotate parameters in D like that 
without changing calling semantics to document that they are 
input only parameters and potentially allow optimizations?