如何提升运营商的工作？ [英] How do boost operators work?

问题描述

的boost ::运营商自动基于手动实现比如 +定义操作符，如 + = 这是非常有用的。要生成 T 的经营者，一个来自继承的boost ::符＆LT; T＆GT; 如由升压例如：

boost::operators automatically defines operators like + based on manual implementations like += which is very useful. To generate those operators for T, one inherits from boost::operators<T> as shown by the boost example:

类敏：升压::经营者＆LT;＆敏GT;

我熟悉的CRTP模式，但我看不出它是如何工作在这里。具体来说，我真的没有任何继承自设施的运营商不成员。 的boost ::运营商似乎是完全空的，但我不是很擅长阅读提振源$ C ​​$ C。

I am familiar with the CRTP pattern, but I fail to see how it works here. Specifically, I am not really inheriting any facilities since the operators aren't members. boost::operators seems to be completely empty, but I'm not very good at reading boost source code.

谁能解释这是如何工作的细节？是这种机制公知和广泛使用的

Could anyone explain how this works in detail? Is this mechanism well-known and widely used?

推荐答案

有一个大的多重继承链，其中在顶部有一些实现经营类，但这样做朋友的功能，从而将它们放置在封闭的空间，而不是作为类的成员。

There's a big multiple inheritance chain, at the top of which there are a number of classes that implement the operators, but do so as friend functions, thus placing them in the enclosing namespace rather than as members of the class.

例如，最终实施运营商+ 变成了：

For example, the final implementation of operator+ becomes:

template <class T, class U, class B = ::boost::detail::empty_base<T> >
struct addable2 : B
{                                                                  
  friend T operator +( T lhs, const U& rhs ) { return lhs += rhs; }
  friend T operator +( const U& lhs, T rhs ) { return rhs += lhs; }
};

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