abstract fun put(key: K, value: V): V?
(Common source) (JVM source) (JS source) (Native source)
For Common, JVM
Associates the specified value with the specified key in the map.
This method is redeclared as abstract, because it's not implemented in the base class, so it must be always overridden in the concrete mutable collection implementation.
Return the previous value associated with the key, or
null if the key was not present in the map.