How to iterate over non-const variables in C++?

It does not work because in {a,b} you are making a copy of a and b. One possible solution would be to make the loop variable a pointer, taking the addresses of a and b:

#include <initializer_list>

struct Obj {
    int i;
};

Obj a, b;

int main() {
    for(auto obj : {&a, &b}) {
        obj->i = 123;   
    }
}

See it live

Note: it is generically better to use auto, as it could avoid silent implicit conversions