std::experimental::ranges::Mergeable
来自cppreference.com
                    
                                        
                    < cpp | experimental | ranges
                    
                                                            
                    |   template < class I1, class I2, class Out, class R = ranges::less<>,            class P1 = ranges::identity, class P2 = ranges::identity >  | 
(范围 TS) | |
Mergeable 概念指定通过复制元素,归并排序序列到输出序列中的算法(例如 ranges::merge )的常用要求。