put

abstract actual fun put(key: K, value: V): V? (source)

Overrides MutableMap.put

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.