System and method for implicit downcasting at compile time in a data flow program. A first data flow function in an object-oriented dataflow program is identified, where the first function includes an input of a parent data type and an output of the parent data type. The first function is analyzed to determine if the output preserves the run-time data type of the input. A second dataflow function in the object-oriented data flow program is identified, where the second function includes a program element that calls the first function, passing an input parameter of a child data type of the parent data type as input. If the analysis determines that an output parameter returned by the output of the first function will always be of the child data type, the program element is automatically configured at compile time to always downcast the output parameter from the parent data type to the child data type at run-time.