A reason to make friend function with default argument a definition

Asked Nov 02 '18 at 13:13

Active Nov 03 '18 at 08:50

Viewed 39 times

class C {
    friend void f(int = 42);
};

gives me an error:

 friend declaration specifying a default argument must be a definition

What is the reason to prevent only declaration here? In which situation it can be an issue if it would be allowed?

edited Nov 03 '18 at 08:50

Azat Ibrakov

asked Nov 02 '18 at 13:13

αλεχολυτ

@Slava the old post doesn't answer my question. I know that this is forbidden, but for what reason? – αλεχολυτ Nov 02 '18 at 13:17
@slava I'm not sure that really answers the Q. It quotes the part of the standard that causes the error but doesn't attempt to answer why this is required. – NathanOliver Nov 02 '18 at 13:17
Friend *"visibility"* is complex. I care that we might have trouble (when definition doesn't have default). – Jarod42 Nov 02 '18 at 13:17
2

@OP your looking for a technical reason, not a because the standard says so reason, right? – NathanOliver Nov 02 '18 at 13:18
@NathanOliver reason "because standard says so" is good enough for me. You are free to vote for reopen though. – Slava Nov 02 '18 at 13:20
2

Second dup's answer has a link to a C++ DR with some reasoning. – Mat Nov 02 '18 at 13:21
I made the second dupe target the only one as it has the reason why the standard has the wording it does. – NathanOliver Nov 02 '18 at 13:25
1

Direct link to the DR: http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#136 – Jarod42 Nov 02 '18 at 13:30
@NathanOliver yep. I would like to know why, i.e. any possible problem if it would be allowed. – αλεχολυτ Nov 02 '18 at 13:35

0 Answers0