Exer14_53.cpp

// Warning: this is for verification. It cannot compile.
#include <cstddef>
class SmallInt {
    friend SmallInt operator+(const SmallInt&, const SmallInt&);
public:
    SmallInt(int = 0) {} // conversion from int
    operator int() const { return val; } // conversion to int
private:
    std::size_t val;
};
SmallInt operator+(const SmallInt &lhs, const SmallInt &rhs)
{
    return lhs.val + rhs.val;
}
int main()
{
    SmallInt s1;
    double d = s1 + 3.14;
    // error: ambiguous call. There are two viable functions:
    // SmallInt operator+(const SmallInt&, const SmallInt&); 3.14 is converted to int and then SmallInt
    // built-in operator+(int, double); s1 is converted to int
    // To make it legal, we can write as below
    SmallInt s2;
    double d2 = s2.operator int() + 3.14;
    SmallInt s3;
    double d3 = s3 + SmallInt(3.14);
    return 0;
}