Take _any_ element from HashMap: Option<(K, V)>

Is there an idiomatic way to take any value from a HashMap (I don't care which one). None if HashMap is empty.

This function would have type signature &mut self -> Option<(K, V)>. I searched HashMap in std::collections - Rust but found pub fn remove_entry<Q: ?Sized>(&mut self, k: &Q) -> Option<(K, V)> which requires a key.

Context: I'm using a HashMap to represent a set of named consumers; and when something is ready, I want to send it to some consumer, I don't care which one.

If your key can be cheaply cloned, you could call keys().next(), then clone and remove it.

Do you still need the map to be otherwise usable as a normal map when you're in this phase? If you're allowed to fully consume it, then you can just keep its IntoIter and pick off items one by one.

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I forgot to state: I also need to be able to add to this HashMap as well; so the ops are :

  • add new named consumer
  • remove some consumer (don't care which key)
  • remove particular consumer (by key)

If it doesn't have to be HashMap exactly, then you could use IndexMap and its pop() method. You can also use swap_remove_index on a randomly chosen index in 0..len(), if you don't want to be biased toward the last insertion.