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Subject: Unqualified name lookup of names used in a definition of a member of a namespace.
From: Vladimir Grigoriev (vlad.moscow_at_[hidden])
Date: 2020-05-27 19:05:40


According to the C++ 20 Standard (6.5.1 Unqualified name lookup)
 
14 If a variable member of a namespace is defined outside of the scope of its namespace then any name that appears in the definition of the member (after the declarator-id) is looked up as if the definition of the member occurred in its namespace. 
 
Now let’s consider the following program
 
#include <iostream>
 
namespace N1
{
    namespace N2
    {
        int i = 10;
    }
    using namespace N2;
    namespace N3
    {
        extern int x;
    }
    inline namespace N4
    {
        int j = 20;
    }
}
 
int i = 1;
int j = 2;
int N1::N3::x = i + j;
 
int main()
{
    std::cout << "N1::N3::x = " << N1::N3::x << '\n';
}
 
The MS Visual C++ 2019 produces the following result
 
N1::N3::x = 30
 
So several questions arise. The first one is the program valid? That is are the variable declarations
 
int i = 1;
int j = 2;
 
are visible in the this declaration
 
int N1::N3::x = i + j;
?
 
That is if the definition «occurs» in the namespace (according to the quote) then the names are not visible. If I am wrong then should the value of the variable x be equal to 12?  Is it a bug of the compiler that outputs the value of x equal to 30?
 
With best regards,
(Vlad from Moscow)
 
You can meet me at http://cpp.forum24.ru/ or www.stackoverflow.com or http://ru.stackoverflow.com



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