Re: Re: Parsing conditional expressions

[Lorand]

I need this to match some packets stored in XML (actually PDML) format. I use XML::Parser to parse the document, and when I detect an end tag </packet> I want to see if that packet meets some conditions or not.

I need this to determine some phases of the packet flow, so I will have about 6 packet types that have to be matched, and that has to be extensible and easily modifyable, so I don't want to hardcode it. Security is not a concern, it's for a personal project.

Thanks for the answers so far.

[dragonchild]

Create a class called Packet and subclasses called Packet::TypeA, Packet::TypeB, etc. Then, using a factory, create the appropriate subclass. Have each subclass know how to validate itself. No need for eval.

[Lorand]

OK, I didn't think of this, it seems to be the best solution, however I don't know what a factory is, and couldn't find anything that would make that clear... Could you point me to some relevant documentation, maybe a place with examples?

[dragonchild]

A factory is a class or object that creates objects. It's a design pattern. Try googling for "object factory design pattern perl". The first several links look good.

The basic concept is that you ask the factory for an object given a set of parameters and it returns back an object of the appropriate class(es), if possible.