operator overloading in c++

overloading operators

Overloading operators in a language, allows to provide the custom implementation of operators for operands of user-defined types.

One usage Example is to compare instances of a user-defined type, for example a comparision of custom Date-objects, with overloaded + and comparsion <= operators:

auto today = Date(); 
auto fooday = Date(); 

// instead of fooday.AddDays(2),
// handle Date like a primitive type
fooday = fooday + 2; 

if (today <= fooday) {
  // true
  std::cout << "remember fooday is in {foo} days"; 

Comparison of Objects, Operator overloading also enables sort, to return a List of objects in a sorted order.

// timestamp is a private member of Date 
bool Date::operator<= (const Date &d) const {

// and operators in symetric fashion `>`, and for `+`: `-`     

A std Example is string concation.
+ to concat strings and += modifies the string-object itself.

std::string toplevel{"com"};
std::string hostname; 
// the rvalue references modify the moved string:
hostname = "www." + "example." + toplevel;

C++ Core Guidelines: Rules for Overloading and Overload Operators

User-defined operators

User-defined operators in a language would support missing operators.

For example instead of pow(a,b): a pow b or a ** b.
Algol68 showed one way to support user-defined operators.
It can be done, but Readability, Complexity of Syntax (are operators restricted to a set of characters or prefixed), and Precedence are the reasons why C++ does not support user-defined operators.

Written on October 18, 2020
[ c++  ]