An annoyance I have is "add" does not return a boolean indicating if the set already contains the entry. Most runtimes do this to prevent the need for a double

An annoyance I have is "add" does not return a boolean indicating if the set already contains the entry. Most runtimes do this to prevent the need for a double lookup cost by doing "has" then "add." It's a common pattern for when the set is used to either know when to or when not to do expensive work.