Question

When compiling the following:

template <class T>
class Number
{
    private:
        T num;
    public:
        Number() {}
        Number( T n ) : num(n) {}
        operator T() const { return num; }
};

int main()
{
    Number<int> n=5;
    Number<char> c=4;
    int i;

    c=int(5);
    i=n;
    c=n;

    return 0;
}

The compiler gets stuck at the third assignment saying there is no match for operator= in c=n. Shouldn’t n get converted to int, which in turn will be assigned to c?

Answer 1

According to the standard, at most one user-defined conversion (constructor or conversion function) is implicitly applied to a single value. Here, you are expecting the compiler to apply the constructor for Number<char> and the conversion operator for Number<int>. See: https://stackoverflow.com/a/867804/677131.