DMD: invalid UTF character `\U0000d800`

[Per Nordlöw]

On Saturday, 7 November 2020 at 17:49:54 UTC, Jacob Carlborg 
wrote:
> [1] https://en.wikipedia.org/wiki/UTF-16#U+D800_to_U+DFFF

Thanks!

I'm only using these UTF characters to create ranges that source 
code characters as checked against during parsing. Therefore I 
would like to just convert these to a `dchar` for now using a 
`cast`. Can I just do, for instance,

     cast(dchar)0x0000d8000

for

     `\U0000d800`

to accomplish this?