On Dienstag, 27. März 2018 17:32:11 CEST Hans-Christian Stadler wrote:
> I've got a piece of code which I think should be legal, but I get an
> error with g++
>
> #include <iostream>
>
> class bird_watch {
> friend int register_bird() {
> return ++bird_watch::counter;
> }
> static int counter;
> };
>
> int main (int argc, char *argv[])
> {
> std::cout << register_bird() << '\n';
> }
>
> As far as my limited C++ knowledge goes, register_bird should be a valid
> function in global scope?
No, it's in the scope of bird_watch. It's a so-called "private friend" (apart
from being actually private in the snippet you show). Those functions can only
be found via ADL. Example:
struct A {
friend void f(A) {}
};
void g() {
f(A()); // looks in the scope of A because of the argument
}
Cheers,
Matthias
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Dr. Matthias Kretz https://kretzfamily.de
GSI Helmholtzzentrum für Schwerionenforschung https://gsi.de
SIMD easy and portable https://github.com/VcDevel/Vc
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