c++ - Why and when does the ternary operator return an lvalue?

Question

For a long time I thought that the ternary operator always returns an rvalue. But to my surprise it doesn't. In the following code I don't see the difference between the return value of foo and the return value of the ternary operator.

#include <iostream>
int g = 20 ;

int foo()
{
    return g ;
}

int main()
{
    int i= 2,j =10 ;

    foo()=10 ; // not Ok 
    ((i < 3) ? i : j) = 7; //Ok
    std::cout << i <<","<<j << "," <<g << std::endl ;
}

question from:https://stackoverflow.com/questions/54688464/why-and-when-does-the-ternary-operator-return-an-lvalue

Answer 1

Both i and j are glvalues (see this value category reference for details).

Then if you read this conditional operator reference we come to this point:

4) If E2 and E3 are glvalues of the same type and the same value category, then the result has the same type and value category

So the result of (i < 3) ? i : j is a glvalue, which can be assigned to.

However doing something like that is really not something I would recommend.