没有运算符“=”与这些操作数匹配。我超载了它，但它似乎无法正常工作

问：

我已经重载了“=”运算符以接受我的类rational的对象，但它似乎不起作用。这是我的标题和我的类定义

#include <iostream>
#include <assert.h>
#include <fstream>
using namespace std;

class rational {
public:

rational();
rational(int numerator, int denominator);
rational(const rational& r);

int numerator() const;
int denominator() const;

const rational& operator = (const rational& rhs);  //this is what I'm having issues with

private:

int myNumerator, myDenominator;

void reduce();
};

这是我的重载实现（我在主要下面）：

const rational& rational::operator = (const rational& rhs) {
if (*this != rhs) { //added asterisk, otherwise operator would not work
    myNumerator = rhs.numerator();
    myDenominator = rhs.denominator();
}
return *this;
}

下面，我在以下实现中使用“=”运算符时遇到了问题：

istream& operator>>(istream& is, const rational& r) {
    char divisionSymbol;
    int numerator = 0, denominator = 0;

    is >> numerator >> divisionSymbol >> denominator;
    assert(divisionSymbol == '/');
    assert(denominator != 0);
    rational number(numerator, denominator);
    r = number; /* Error: no operator matches these operands (more specifically no operator found
 which takes a left-hand operand of type 'const rational') but I am unsure how to fix that as the
 assignment operator only takes one parameter (unless I am mistaken)*/
    return is;
}

我一辈子都想不出什么不起作用，可能是语法问题？而且我的教授很老派，所以可能是一种过时的做法？任何提示将不胜感激。