const and immutable values, D vs C++?

[Ola Fosheim Grøstad]

On Wednesday, 4 December 2019 at 22:51:01 UTC, Ola Fosheim 
Grøstad wrote:
> Is there a way to specify in generic code that you want the 
> best fit of a const/immutable reference depending on the return 
> type (but not a mutable one)?

I mean, if f() return mutable or const then it should be const, 
but if it returns immutable then it should be immutable. 
Something like:

readonly myref = f()