As per rule number 4 of Object Calisthenics by Jeff Bay (RTF) in The ThoughtWorks Anthology, it is recommended that one should "Use first-class collections".
Rule 4: First class collections
Application of this rule is simple: any class that contains a collection should contain no other member variables. Each collection gets wrapped in its own class, so now behaviors related to the collection have a home. You may find that filters become a part of this new class. Also, your new class can handle activities like joining two groups together or applying a rule to each element of the group.
What I could understand from this was that we should use a separate class wrapping up the collection and with methods to add,delete modify data of that collection.
and We need this so that we are sure of what datatype goes into the collection and what comes out.
In case we use generic collection (in languages where it is applicable), do we need to follow this rule?
If I am missing an important significance, please clarify.