Problems with `Menu`? about ftxui HOT 2 OPEN

This might be a bit costly to call the functor everytime we need to observe the list size.

I was thinking adding an option to ConstStringListRef to provide class implementing the required functions.

class ConstStringListRefAdapter {
  virtual int Size() = 0;
  virtual const std::string Entry(int index) = 0;
}

ConstStringListRef(ConstStringListRefAdapter* adapter);
ConstStringListRef(std::unique_ptr<ConstStringListRefAdapter> adapter);

But I am not totally convinced.

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You're right the ConstStringListRefAdapter stills creates a new string each time so that would very bad for performance, what about a vector<std::string_view>? You still have the hit when you compute the size but it's better I think.
I also thought of using vector<std::string*>, I don't know how much change would be required to the existing code, so tell me what you think about the two suggestions.

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