7.1Defining Abstract Data Ty &7.3Additional Class Features &7.5

• Objects that are const, and references or pointers toconstobjects, maycall onlyconstmember functions.

• The IO classes aretypes that cannot be copied, so we may only pass them by reference

  
  

  
  

• A mutabledata memberis never const, even when it is a member of aconstobject. Accordingly, aconstmember function may change amutablemember. 

  
  

• in-class initializers must use either the=form of initialization (whichwe used when we initialized the the data members ofScreen) or the direct form ofinitialization using curly braces (as we do forscreens). 

  
  

• We can prevent the use of a constructor in a context that requires an implicitconversion by declaring the constructor asexplicit: 

  class Sales_data { public:Sales_data() = default;Sales_data(const std::string &s, unsigned n, double p):bookNo(s), units_sold(n), revenue(p*n) { } explicit Sales_data(const std::string &s): bookNo(s) { } explicit Sales_data(std::istream&);// remaining members as before

  <span style="font-family: Arial, Helvetica, sans-serif;">};</span>