B.20. ReferencesPerl'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 OO programming and complex data structures, among other tricks. See the perlreftut and perlref manpages. The Alpaca covers references in great detail. B.20.1. Complex Data StructuresReferences 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.[
B.20.2. Object-Oriented ProgrammingYes, Perl has objectsit's buzzword-compatible with all of those other languages. OO programming lets you create your own user-defined datatypes with associated abilities, using inheritance, overriding, and dynamic method lookup.[
B.20.3. Anonymous Subroutines and ClosuresOdd 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. Again, this is covered in the Alpaca book. |