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Re: [std-proposals] Should every declaration that using-declarator declared should be accessible?

From: Arthur O'Dwyer <arthur.j.odwyer_at_[hidden]>
Date: Mon, 28 Jun 2021 10:17:35 -0400
On Mon, Jun 28, 2021 at 3:26 AM chuanqi.xcq via Std-Proposals <
std-proposals_at_[hidden]> wrote:
> I am cleanning some codes with the warning of overloaded virtual
> Here is the introduction for overloaded virtual functions:
> At first, I thought it is a compiler bug.
> However, I find these words in 9.9.14 N4878,
> "In a using-declarator that does not name a constructor, every
declaration named shall be accessible."

It took me a while to understand your example. Eventually I got it:
Class `A` has overloaded public and private constructors, and overloaded
public and private `get` methods.
Class `B` can say `using A::A;` just fine. But it can't say `using
A::get;`. This feels inconsistent.

However, `using A::A` does something very different from `using A::get`.
When you inherit constructors with `using`, you're doing it because
constructors are not ordinarily inherited at all. When you `using` the name
of an ordinary member function, it's not "to inherit them," because
ordinary member functions are already inherited just fine; it's rather
because you want to change the access control of the existing names.

In Chuanqi's specific case, the right refactoring is not to use `using` — I
mean, to a first approximation, using `using` is *never* appropriate
in modern C++! The right refactoring is to eliminate the combination of
overloading and virtual methods. Virtual methods aren't called directly by
the client (because Non-Virtual Interface Idiom), so you're in control of
these names, so you can give them whatever names you choose. For example,
"virtual void *getByName(char *)" and "virtual void *getByNameAndIndex(char
*, int)". Then the names don't collide, so there's no name hiding, so you
don't have to work around anything at all.
See also "When Should You Give Two Things the Same Name?"
<https://www.youtube.com/watch?v=OQgFEkgKx2s&ab_channel=CppNow> (CppCon
2021), which coincidentally "premieres in 3 hours from now" according to


Received on 2021-06-28 09:17:48