Set aside all the wisecracks about Perl being unmaintainable or useful only for small scripts. Also be prepared to renounce the widely held assumption that it’s not a truly object-oriented language. In this section we will develop a general Perl framework that will let you quickly add new features to applications and adapt applications to changing database structures.

The code that follows is complex and requires an in-depth knowledge of Perl. Among the features of Perl we exploit are references, recursion, variable type checking, function argument manipulation (the $_[0] syntax), dynamic array building through push statements, and multidimensional hashes—and of course, lots of object-oriented techniques. These features are amply explained in other Perl books, notably Programming Perl by Larry Wall, Tom Christiansen, and Jon Orwant (O’Reilly).