Perl's references are similar to C's pointers, but in operation, they're more like what you have in Pascal or Ada. A reference "points" to a memory location, but because there's no pointer arithmetic or direct memory allocation and deallocation, you can be sure that any reference you have is a valid one. References allow object-oriented programming and complex data structures, among other nifty tricks. See the perlreftut and perlref manpages.
B.20.1. Complex Data Structures
References allow us to make complex data structures in Perl. For example, suppose you want a two-dimensional array? You can do that, or you can do something much more interesting, like have an array of hashes, a hash of hashes, or a hash of arrays of hashes. See the perldsc (data-structures cookbook) and perllol (lists of lists) manpages.
B.20.2. Object-Oriented Programming
Yes, Perl has objects; it's buzzword-compatible with all of those other languages. Object-oriented (OO) programming lets you create your own user-defined datatypes with associated abilities, using inheritance, overriding, and dynamic method lookup.
Unlike some object-oriented languages, though, Perl doesn't force you to use objects. (Even many object-oriented modules can be used without understanding objects.) But if your program is going to be larger than N lines of code, it may be more efficient for the programmer (if a tiny bit slower at runtime) to make it object-oriented. No one knows the precise value of N, but we estimate it's around a few thousand or so. See the perlobj and perlboot manpages for a start, and Damian Conway's excellent Object-Oriented Perl (Manning Press) for more advanced information.
B.20.3. Anonymous Subroutines and Closures
Odd as it may sound at first, it can be useful to have a subroutine without a name. Such subroutines can be passed as parameters to other subroutines, or they can be accessed via arrays or hashes to make jump tables.
Closures are a powerful concept that comes to Perl from the world of Lisp. A closure is (roughly speaking) an anonymous subroutine with its own private data.
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