Let T be a user defined type that has an instance method IM . Let IT be a scalar expression having a compile time type of T .

IT.IM ( [ parameter, .... ] )

This will call the instance method IM of T and will return whatever the IM returns.

Similarly to member observers/mutators the compile time type of IT can be specified explicitly:

(IT as T).IM ( [ parameter, .... ] )

This syntax however has an additional property in that it will call the method of the type regardless of whether it is overloaded in a subtype or not. Let ST be a subtype of T and ST that has the method IM overloaded. Let IST be a scalar expression that represents an instance of ST .

Then:

(IST as T).IM ( [ parameter, ... ] )

will call the method IM as defined in T , whereas

IST.IM ( [ parameter, ... ] )

will call the method IM as defined in ST .

CREATE TYPE UDT_BASE
  method A () returns integer;

CREATE TYPE UDT_SUB under UDT_BASE
  OVERRIDING method A () returns integer;

create method A () returns integer for UDT_BASE
{
  return 1;
}

create method A () returns integer for UDT_SUB
{
  return 2;
}

select new UDT_SUB ().A() as IMPLICIT,
  (new UDT_SUB() as UDT_BASE).A() as EXPLICIT;

IMPLICIT                EXPLICIT
----------------------------
2                       1