The document discusses operator overloading in C++. It provides examples of overloading operators like ++, [], and == for an enumeration of months to provide more natural syntax when working with the enum. Operator overloading allows defining operators for user-defined types to provide conventional operator meanings and make code more clear and efficient. It can be used to define operations for enumerations that are less error-prone than alternative approaches like switch statements or functions.

1. Operator Overloading
Dustin Chase
C++ Lightning Talks
December 14, 2015

2. Outline of Presentation
 Introduction
 Enumeration
 Operator Overloading
 Operator Overloading In Action
 Closing Thoughts

3. Introduction
 Who am I?
 Expected Background/Audience
 Source Material

4. Enumeration
 Enumeration (enum): A very simple user-defined type, specifying its
set of values (its enumerators) as symbolic constants.
enum class Card {copper, silver, gold, council_room, …};
if (card_played == Card::copper) {
copperAction();
}

5. Operator Overloading
 Operator Overloading: Define almost any C++ operator for class or
enumeration operands.
 Provide conventional notation for a type we design
 “+” means add, “=“ means assignment
 Convenience, Efficiency, Clarity

6. Enumeration and Overloading Together
 Example enumeration:
enum class Month {
Jan=1, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec
};
 Next month?

7. A Function!
Month nextMonth(const Month &m) {
switch (m)
{
case(Month::Jan):
return Month::Feb;
break;
case(Month::Feb):
return Month::Mar;
break;
…
}
}
 Lots of code to write – error prone
 Not as convenient for users of your code
 What does nextMonth(const Month &m)
do?

8. Operator Overload!
Month& operator++(Month &m) {
m = (m==Month::Dec) ? Month::Jan : Month(int(m) + 1);
return m;
}
Month end = Month::Jan;
++end;
//vs. end = nextMonth(end);
//More natural to read than a series of function calls

9. ++ Operator Usage
for (Month n = Month::Jan; n < Month::Dec; ++n) {
cout << int(n) << endl;
}

10. Another example: ‘[]’ operator
 C++ strings
string name = “William”;
name[3] = ‘x’;
//name is now “Wilxiam”;
 Saves us from iterating through the string object, or using some
combination of other functions

11. Closing
 Enum helps make your code readable
 Card::copper vs. 7 (magic number)
 Operator overloading as well
 Define operators only with conventional meaning
 “+” should mean addition, not “tooblekane”
 Don’t define operators for a type unless you’re sure it will make
positive changes to your code
 The most interesting operators aren’t +, -, * and /, but =, ==, !=, [] and
().