Is there any good reason why C++ namespaces are "closed" in D?

[Seb]

On Sunday, 29 July 2018 at 08:28:08 UTC, Walter Bright wrote:
> On 7/29/2018 1:15 AM, Manu wrote:
>> All we're asking for is that C++ namespaces do **nothing** 
>> except affect the mangling.
>
> If I do that, the next bug report will be:
>
>   extern (C++, "ab") { void foo(); }
>   extern (C++, "cd") { void foo(); } // Error, foo() is already 
> declared
>
>   foo(); // which one gets called?
>
> The reason namespaces were added to C++ is to not have such 
> name collisions. Namespaces in C++ introduce a scope. D cannot 
> interoperate with this without introducing a scope as well.

FYI: this doesn't error as of now, but with 
https://github.com/dlang/dmd/pull/8429 it will.