Friend Function vs. Member Function for Operator Overloading: When is a Friend Function Preferred for `

Operator Overloading: Friend Function vs. Member Function for "<<"

In C , overloaded operators can be implemented either as friend functions or member functions. When it comes to the stream insertion operator "<<," certain considerations guide the choice between these approaches.

Using a Friend Function

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

This approach is commonly used for stream operators because:

• It allows access to the stream object (os), which is necessary for performing the stream insertion.
• It follows the convention of stream operators returning a stream reference for chaining purposes.

Using a Member Function

ostream & operator<<(Paragraph const& rhs);

While it's tempting to think that member functions should be used for all class methods, this approach is not recommended for the "<<" operator for several reasons:

• You cannot access the stream object (os) from a member function.
• You would need to manually call the "to_str" method in the member function, which is redundant and error-prone.
• It's not conventional for stream operators to be member functions.

Example

Consider the following class:

class Paragraph {
    std::string m_para;

public:
    Paragraph(std::string const& init) : m_para(init) {}

    std::string const& to_str() const { return m_para; }
};

Rationale

In this case, using a friend function for the "<<" operator is the preferred choice because:

• It provides access to the stream object (os) for streaming.
• It follows the convention of stream operators returning a stream reference.
• It reduces code duplication and potential errors compared to using a member function.

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