Mastering the C++17 STL

Moving elements without moving them

Recall that, with std::list, we were able to splice lists together, move elements from one list to another, and so on, by using the "particular set of skills" of std::list. As of C++17, the tree-based containers have acquired similar skills!

The syntax for merging two sets or maps (or multisets or multimaps) is deceptively similar to the syntax for merging sorted std::list:

    std::map<std::string, std::string> m = {      {"hello", "world"},      {"quick", "brown"},    };    std::map<std::string, std::string> otherm = {      {"hello", "dolly"},      {"sad", "clown"},    };    // This should look familiar!    m.merge(otherm);    assert((otherm == decltype(m){      {"hello", "dolly"},    }));    assert((m == decltype(m){      {"hello", "world"}, {"quick", "brown"}, ...