What is the key/value requirements for these maps?

[afshinpir]

Hi

I wonder what is the requirements for the key/value of these maps. For example, can I use them with a structure like this as value?

struct S {
    S(int i) : m_(i) {}
    std::atomic<int> m_;
};

As you see, this structure is not copy/move constructible/assignable. I can use this with std::unordered_map, but I wonder if I can use such structure an my map value.

[greg7mdp]

Hi @afshinpir, thanks for the question. Because std::atomic is not movable, you won't be able to use use it in flat hash maps (where the values are moved when the map resizes), but you should be able to use them in phmap's node hash map, for example in phmap::node_hash_map.

[afshinpir]

@greg7mdp Thanks for the info.