What restrictions can be applied on stored functions, which are called from SQL statements? | PL SQL

 The main restrictions on stored functions that are called from SQL statements are:
a.    These functions can use only positional methods for passing the parameters.
b.    These functions can use only SQL specific datatypes. PL/SL datatypes, such as RECORD or TYPE, cannot be used.
c.    User should have EXECUTE privilege on the function to use it within SQL statements
d.    These functions cannot have the OUT and IN OUT parameter modes.