Advanced Perl Programming

Streamed Data

We look at three modules, FreezeThaw, Data::Dumper, and Storable, in this section. All of them serialize Perl data structures to ASCII or binary strings; only Storable actually writes them to disk. The other two modules are important because they can be used in conjunction with other persistence mechanisms such as databases and DBM files. All of them correctly account for blessed object references and self-referential data structures, but trip up when it comes to typeglobs, tied variables, or scalars containing pointers to C data types (justifiably so). It is also impossible for these (or any) modules to understand implicit relationships. For example, if you use the ObjectTemplate approach described in Section 8.1, the “object” is basically an array index, and so the disk will get to see only a bunch of meaningless array indices minus the data. Another subtle error occurs when you use references as hash indices and Perl converts them to strings (such as SCALAR(0xe3f434)). This is not a real reference, so if you store the hash table to a file and recreate it, the implicit reference to the original structure is not valid any more.

Moral of the story: simple nests of Perl structures are handled easily; in all other cases, it is your responsibility to translate your application data into a structure containing ordinary Perl elements before sending it to disk.

FreezeThaw

FreezeThaw, written by Ilya Zakharevich, is a pure Perl module (no C extensions) and encodes complex ...