小编jas*_*son的帖子

以下示例来自"Programming in Scala"一书.给定一个类'Rational'和以下方法定义:

def add(that: Rational): Rational =
    new Rational(
        this.numer * that.denom + that.numer * this.denom,
        this.denom * that.denom
    )

我可以使用带有Int参数的便捷版本成功地重载add方法,并使用上面的定义:

def add(that: Int): Rational =
    add(new Rational(that, 1))

到目前为止没问题.

现在,如果我将方法名称更改为运算符样式名称:

def +(that: Rational): Rational =
    new Rational(
        this.numer * that.denom + that.numer * this.denom,
        this.denom * that.denom
    )

像这样过载:

def +(that: Int): Rational =
    +(new Rational(that, 1))

我得到以下编译错误:

(fragment of Rational.scala):19: error: value unary_+ is not a member of this.Rational
+(new Rational(that, 1))
 ^

为什么编译器要查找该+ …