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

[Atila Neves]

On Monday, 30 July 2018 at 19:51:09 UTC, Walter Bright wrote:
> On 7/30/2018 6:45 AM, Atila Neves wrote:
>> On Friday, 27 July 2018 at 22:50:20 UTC, Walter Bright wrote:
>>> On 7/27/2018 10:28 AM, Atila Neves wrote:
>>>> But all I'm trying to do here is tell the D compiler how to 
>>>> mangle symbols.
>>>
>>> Namespaces have semantic implications, too, such as overload 
>>> resolutions. A namespace introduces a new scope, not just a 
>>> mangling.
>> 
>> Should they, though?
>
> They do in C++. That was the whole point of adding namespaces:
>
> C:    void ns_foo();
> C++:  namespace ns { void foo(); }

I meant "should they in D, though?". I don't want to import C++ 
semantics into D. I want D to correctly mangle C++ namespaced 
functions and change nothing at all about overload resolution in 
D.

>> Structs aren't namespaces, I wouldn't expect them to behave 
>> the same.
>
> From a language perspective, they are namespaces.

Technically, yes. But not C++ namespaces.

> C++ has a lot of bizarre name lookup behavior.

It does. I don't think anyone is suggesting we copy it.

>> I didn't know about this and it makes things better, but it's 
>> not a real solution to my problem.
>
> See my other post doing this same thing with structs.

It's not the same - if I want to link to std::vector and 
std::string, I'd expect them to be used in D as std.vector and 
std.string, not std.vector and HackyDThing0.std.string.


>> I'm arguing that reopening should be allowed.
>
> As detailed in another post, this opens a whole host of other 
> problems. Even in C++, what names are visible in a namespace at 
> any particular point in the compilation is a nebulous concept. 
> (It is actually carefully specified, but you have to be a 
> language lawyer / compiler implementer to know what they are - 
> to the user it is erratic, random, and nebulous.)

Right, but D doesn't have to do any of that - as far as D is 
concerned it's just mangling. Well, as far as the typical D user 
that writes `extern(C++)` anyway.