Isn't the const modifier here unnecessary? [duplicate]

Answer 1

The const modifier on the return value is not necessary and can hinder move semantics. The preferred way of preventing assignment to rvalues in C++11 is to use "ref-qualifiers."

struct Rational
{
  Rational & operator=( Rational other ) &; // can only be called on lvalues
};

Rational operator*( Rational const & lhs, Rational const & rhs );

Rational a, b, c;

(a * b) = c; // error