操作符在类外重载 [英] Operator overloading outside class
问题描述
有两种方法可以重载C ++类的操作符:
There are two ways to overload operators for a C++ class:
class Vector2
{
public:
float x, y ;
Vector2 operator+( const Vector2 & other )
{
Vector2 ans ;
ans.x = x + other.x ;
ans.y = y + other.y ;
return ans ;
}
} ;
课外
Outside class
class Vector2
{
public:
float x, y ;
} ;
Vector2 operator+( const Vector2& v1, const Vector2& v2 )
{
Vector2 ans ;
ans.x = v1.x + v2.x ;
ans.y = v1.y + v2.y ;
return ans ;
}
(显然在C#中你只能使用外部类方法。
(Apparently in C# you can only use the "outside class" method.)
在C ++中,哪种方式更正确?哪一个是最好的?
In C++, which way is more correct? Which is preferable?
推荐答案
基本问题是你希望在左侧参数中执行转换操作员?如果是,请使用自由功能。
The basic question is "do you want conversions to be performed on the left-hand side parameter of an operator?". If yes, use a free function. If no, use a class member.
例如,对于字符串的运算符+(),我们希望执行转换,因此我们可以这样说:
For example, for operator+() for strings, we want conversions to be performed so we can say things like:
string a = "bar";
string b = "foo" + a;
其中执行转换以将char *foo转换为std :: string。因此,我们使字符串的运算符+()为一个自由函数。
where a conversion is performed to turn the char * "foo" into a std::string. So we make operator+() for strings into a free function.
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