Pipelined functions implicitly create SQL level TYPES

In the "I learn something new every day" category, Solomon Yakobson pointed out something in a post on the Quest Pipelines forum, "under PL/SQL Tables, Nested Tables, & VARRAYS » Problem in executing Function which returns collection".

Apparently, under the sheets a PIPELINED function will create SQL types and collection types.

If you run...

CREATE OR REPLACE PACKAGE PFP_CONSTANTS_PKG IS
TYPE v_rec IS RECORD
 (
   v_date DATE,
   v_mon NUMBER(2)
 );
 TYPE v_array IS TABLE OF v_rec;
 function dummy return v_array pipelined;
END;
/

and then check USER_TYPES, you'll find that it creates three types prefixed by SYS_PLSQL_, followed by a number (which looks like it corresponds to the OBJECT_ID visible in USER_OBJECTS) and the rest of the identifier.

So if you find some types with that sort of prefix, you'll be able to track back to the package which created them.