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Adds a subscription to changes of the contents of the map.

When handler is initially added, it is called receiving all key/value pairs currently in the map. Every time a key/value pair is added to the map, the handler is called receiving the new key/value pair. The Lifetime instance passed to the handler expires when the key/value pair is removed from the map.

The subscription is removed when the given lifetime expires.

Adds a subscription to changes of the contents of the map, with the handler receiving keys and values as separate parameters.

When handler is initially added, it is called receiving all keys and values currently in the map. Every time a key/value pair is added to the map, the handler is called receiving the new key and value. The Lifetime instance passed to the handler expires when the key/value pair is removed from the map.

The subscription is removed when the given lifetime expires.