Returns a |String| which is a unique identifier of the container type (|List|, |Dict| and |Partial|). It is guaranteed that for the mentioned types id(v1) ==# id(v2) returns true iff type(v1) == type(v2) && v1 is v2. Note that |v:_null_string|, |v:_null_list|, and |v:_null_dict| have the same id() with different types because they are internally represented as a NULL pointers. id() returns a hexadecimal representanion of the pointers to the containers (i.e. like 0x994a40), same as printf("%p", {expr}), but it is advised against counting on the exact format of return value. It is not guaranteed that id(no_longer_existing_container) will not be equal to some other id(): new containers may reuse identifiers of the garbage-collected ones.