Re: [isocpp-modules] Clarification of visibility rules for friend functions

[Richard Smith]

On Tue, Sep 24, 2019 at 4:04 PM David Stone via Modules <mod...@lists.isocpp.org> wrote:

Is it valid to call `get<0>(my::derived<int>())` from an importing module?

Yes. The base class my::base<int> has a reachable definition, so its friend 'get' is visible to ADL by [basic.lookup.argdep]/4.3.

 

export module my;

namespace my {

template<typename>
struct base {
    template<int>
    friend constexpr auto get(base) {
        return 5;
    }
};


export template<typename T>
struct derived : base<T> {
};

} // namespace my

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