c++ - 转换指南

Question

如果您有两个类 A 和 B，并且您需要定义从 A -> B 和 B -> A 的转换，那么标准解决方案是什么？

1. 让 A 有一个构造函数接受 B 和 A 有转换运算符到乙？
2. 让 A 和 B 都拥有对方的构造函数？
3. 让 A 和 B 都具有到另一个的转换运算符？
4. 某种 CPO convert<To>(From)
5. 还有其他办法吗？？？

(注2和注3需要循环依赖)

Answer 1

我在cppslack上问了一圈，好像没有标准/通用的情况，所以归结为这种情况。

(1) is what you do when you're extending an API, i.e. A knows about B but B doesn't know about A;

(2) or (3) is what you do when A and B are defined as part of the same API, i.e. they know about each other;

(4) is how you unify two unrelated APIs, i.e. neither A nor B knows about the other.