Why is this an issue?
Member functions can only be used with an instance of a class. But friend functions can be used with an implicitly converted type. So
loosening access privileges to friend on overloaded binary operators makes them more flexible. Specifically, with a friend
function, the class instance can be on either the right or the left of the operator, but with a member function, it can only be on the left.
This rule raises an issue for all non-friend overloaded binary operators except:
- "
=", "[ ]", and "->", which cannot be overloaded as friend functions.
- "
+=", "-=", "*=", "/=", "%=", "^=", "&=",
"|=", "<<=", and ">>=", which are not symmetric operators.
Noncompliant code example
bool operator==(const MyClass &RHS); // Noncompliant
Compliant solution
friend bool operator==(const MyClass &LHS, const MyClass &RHS);
Resources
