Value checks can be performed before your functions are
executed with removable PRE testing functions. Scalar arguments cannot
be mutated, but object and array reference parameters can, so care must be
taken not to mutate objects and arrays inside the TypeCzech checking functions.
Errors are delivered by non-empty string values, thus a return value of '' indicates
all is well in a PRE or POST checking function. No return value from PRE checking functions is also indicative
of no error.
In the example to the left, two Persons fail the PRE_check_Person() checks:
- Atahualpa does not have a l_name parameter
- Louis' regnal number of XIV is not in the known set