1. Operator Overloads Part2

2. Issue Provide member +(int) operator Rational + int OK int + Rational Error

3. Compiler View What compiler sees r2 + 4 r2.operator+(4) call + function on r2, pass it 4 4 + r2 4.operator+(r2) call + function on 4?!?!?

4. Overload Options Overload operator as member: r1 + r2 interpreted as r1.operator+(r2) Overload operator as non-member: r1 + r2 interpreted as +(r1, r2)

5. Overload Option 2 Provide operator as non-member function r1 + r2 interpreted as +(r1, r2) NOT a member. No Rational::

6. Option 2 Implementation Standard function r1 + r2 interpreted as +(r1, r2) – Need two parameters – No private access

7. Option 2 Advantage Standard function operator can place class last: Compiler view: 4 + r2 +(4, r2) Call + function with 4 and r2

8. Order matters 4 + r2 not the same as r2 + 4

9. Which Option? Implement operators as members or functions? No perfect answer… – Members : Access to private data First operand is implicit – must be your type – Standard function First operand can be other type Normally don't have access to privates…

10. Friends With Benefits Friend's of a class have access to its privates: OK if B is A's friend Private access not allowed

11. Friend + Can declare functions as friends: – Declares function – Makes friend of class – Gives private access:

12. Other Overloads Relational as non-members:

13. Relational Implementation Compare first to second, return true/false Nonmember implementation

14. Type Conversions

15. One arg constructors used for casts and implicit conversions:

16. + int without operator With non-member function, compiler will implicitly construct objects to make operators work:

17. Type Conversions explicit keyword on constructors prevents implicit conversions

18. Type Conversions Conversion operators define how to cast away from Rational – Written as member function – Return type used as operator name

19. Conversions at Work: Any situation requiring primitive, compiler will use conversion operator:

20. Ambiguous Conversions Too many choices confuses compiler: Make things explicit:

21. [ ], >

22. LValues and RValues LValues : Things that can be on left side of = – Variables, other storage RValues : Everything else – Temporary values

23. BAD Subscript Can overload subscript operator – Easy access to member data

24. ??? 2 = 3 r1 numerator2 denominator5

25. BAD Subscript Subscript supposed to produce Lvalue – returned int is not an Lvalue

26. GOOD Subscript Subscript must return a reference

27. r1.numerator = 3 r1 numerator2 denominator5

28. IO Operators Most classes should not do direct IO – No knowledge of context they will be used in toString() function better but clunky

29. IO Operators Most classes should not do direct IO – No knowledge of context they will be used in toString() function better but clunky Want to directly output/input:

30. IO Overloads Stream always left operand of insertion / extraction operators: Must overload > as friends

31. IO Overloads Overloading > – ostream means any output stream File, cout, stringstream… – istream any input stream – Return reference to the stream to allow chaining

32. IO Overloads Overloading > – ostream means any output stream File, cout, stringstream… – istream any input stream – Return reference to the stream to allow chaining cout

33. Output Stream insertion: – Pick info to send to stream – Return the stream (as reference) – Friend, so has private access

34. Input Stream extraction: – Read what you want from stream May discard some – Modify object passed as reference – Return the stream (as reference)

35. Input Stream extraction process: 12/30 rational numerator? denominator?

36. Input Stream extraction process: 12/30 rational numerator12 denominator?

37. Input Stream extraction process: 12/30 rational numerator12 denominator?

38. Input Stream extraction process: 12/30 rational numerator12 denominator30