A customer wanted to sort a Windows Runtime collection. The obvious thing to try is<\/p>\n
template<typename T, typename Compare>\r\nvoid SortObservableVector(\r\n winrt::IObservableVector<T> const& observable,\r\n Compare comp)\r\n{\r\n std::sort(begin(observable), end(observable),\r\n [&](auto&& a, auto&& b)\r\n { return comp(a, b); });\r\n}\r\n<\/pre>\nThis works, but you can do better.<\/p>\n
One problem with this version is that we are operating on an observable vector, which means that every vector operation raises a Vector\u00adChanged<\/code> event, and the observers of this vector will get spammed with events as the sort operation proceeds.<\/p>\nAnother problem is that every operation on the observable vector is a virtual method call. Depending on what you’re sorting, this virtual method call overhead could be insignificant, or it could overwhelm the actual work you’re trying to do.<\/p>\n
One way to avoid both of the problem is to slurp the contents of the observable vector into a std::vector<\/code><\/a>, sort the std::vector<\/code>, and then shove the results back in<\/a>.<\/p>\ntemplate<typename T, typename Compare>\r\nvoid SortObservableVector(\r\n winrt::IObservableVector<T> const& observable,\r\n Compare&& comp)\r\n{\r\n \/\/ Slurp into a vector\r\n std::vector<T> v(observable.Size(),\r\n winrt_empty_value<\/a><T>());\r\n observable.GetMany(0, v);\r\n\r\n \/\/ Sort the vector\r\n std::sort(begin(v), end(v),\r\n std::forward<Compare>(comp));\r\n\r\n \/\/ Shove the results back in\r\n observable.ReplaceAll(v);\r\n}\r\n<\/pre>\n