Friend or Member Function: When Should `operator

When to Implement Operator<< as a Friend or Member Function

Introduction:

Operator overloading allows us to extend operators like << to work with custom classes. The question arises: should operator<< be implemented as a friend function or a member function within the class?

Member Function vs. Friend Function

Member Function

ostream& operator<<(ostream &os, const obj& rhs);

Advantages:

• Direct access to the class's private members
• Encapsulation of streaming logic within the class

Friend Function

friend ostream &operator<<(ostream &os, const obj& rhs);

Advantages:

• Can be used by multiple classes
• Can facilitate automatic type conversion for both operands

Rationale for Decision

Equality Operators

For equality operators (e.g., ==, !=), member functions are preferred because:

• They have direct access to the class's private data.
• They enforce the class's internal representation for equality comparisons.

Stream Operators

For stream operators (<<, >>), friend functions are necessary:

• They operate on objects of different types (e.g., ostream and the custom class).
• They return a reference to the stream object for chained operations.

Example:

Consider a Paragraph class with a private m_para string member. We want to implement operator<< to print the paragraph's text:

class Paragraph {
public:
    Paragraph(const string& init) : m_para(init) {}
    const string& to_str() const { return m_para; }
    bool operator==(const Paragraph& rhs) const { return m_para == rhs.m_para; }
    friend ostream &operator<<(ostream &os, const Paragraph& p);

private:
    string m_para;
};

ostream &operator<<(ostream &os, const Paragraph& p) {
    return os << p.to_str();
}

In this example, operator<< is implemented as a friend function because it operates on different types and returns a stream reference. The to_str() method is used to access the private m_para member and convert it to a string for output.

The above is the detailed content of Friend or Member Function: When Should `operator. For more information, please follow other related articles on the PHP Chinese website!