In § 7.5.4 (p. 294) we saw that a nonexplicit
constructor that can be called with one argument defines an implicit conversion. Such constructors convert an object from the argument’s type to the class type. We can also define conversions from the class type. We define a conversion from a class type by defining a conversion operator. Converting constructors and conversion operators define class-type conversions. Such conversions are also referred to as user-defined conversions.