What are the prominent downsides of the D programming language?

[Jean-Louis Leroy]

On Tuesday, 29 September 2020 at 21:43:03 UTC, mw wrote:
> The key idea is to treat each parent's class attributes 
> individually (via rename/undefine/redefine/select) instead of 
> as in other multiple inheritance languages, e.g. C++'s 
> all-or-none approach, i.e. either all the parents' attributes 
> are shared or separated, and even when separated, there is no 
> proper renaming mechanism to handle it.

If Base has features f and g, and Derived inherits from Base but 
undefines g, I assume that a Derived object cannot be substituted 
for a Base. Correct?