c – 让课程与运算符一起工作的更简单方法?
作者:互联网
在这里,我有一个名为Value的类,它只能获取并设置float.
class Value
{
public:
Value(float f)
:f(f){};
float get()
{
return f;
}
void set(float f)
{
this->f = f;
}
private:
float f;
};
我希望我的班级能够像以下示例一样工作.
Value value(3);
std::cout << value * 2 - 1 << std::endl; // -> 5
std::cout << value == 5 << std::endl; // -> true
value /= 2;
std::cout << value << std::endl; // -> 2.5
我应该手动将所有操作符方法添加到我的类中吗?
或者是否有更容易的解决方案来像浮动一样对待价值?
解决方法:
以下是相关算术,相等和流运算符的惯用实现.
内联评论中的注释.
另请参阅有关允许从float进行隐式转换的后果/好处的说明.
#include <iostream>
class Value
{
public:
// Note - this constructor is not explicit.
// This means that in an expression we regard a float and a Value on the
// right hand side of the expression as equivalent in meaning.
// Note A.
// =
Value(float f)
:f(f){};
float get() const
{
return f;
}
void set(float f)
{
this->f = f;
}
// Idiom: unary operators defined as class members
//
Value& operator *= (Value const& r)
{
f *= r.f;
return *this;
}
Value& operator -= (Value const& r)
{
f -= r.f;
return *this;
}
Value& operator /= (Value const& r)
{
f /= r.f;
return *this;
}
private:
float f;
};
// Idiom: binary operators written as free functions in terms of unary operators
// remember Note A? A float will convert to a Value... Note B
// =
auto operator*(Value l, Value const& r) -> Value
{
l *= r;
return l;
}
auto operator-(Value l, Value const& r) -> Value
{
l -= r;
return l;
}
auto operator<<(std::ostream& l, Value const& r) -> std::ostream&
{
return l << r.get();
}
// Idiom: binary operators implemented as free functions in terms of public interface
auto operator==(Value const& l, Value const& r) -> bool
{
return l.get() == r.get();
}
int main()
{
Value value(3);
// expressions in output streams need to be parenthesised
// because of operator precedence
std::cout << (value * 2 - 1) << std::endl; // -> 5
// ^^ remember note B? value * 2 will resolve to value * Value(2) because of
// implicit conversion (Note A)
std::cout << (value == 5) << std::endl; // -> true
value /= 2;
std::cout << value << std::endl; // -> 2.5
}
标签:c,class,operator-keyword 来源: https://codeday.me/bug/20190828/1746868.html