Collections
This section documents Ruby’s collection
classes. A collection is any class that represents a collection of
values. Array and Hash are the key collection classes in Ruby,
and the standard library adds a Set
class. Each of these collection classes mixes in the Enumerable module, which means that Enumerable methods are universal collection
methods.
Enumerable Objects
The Enumerable
module is a mixin that implements a number of useful methods
on top of the each iterator. The
Array, Hash, and Set classes described below all include
Enumerable and
therefore implement all of the methods described here. Range and IO are other noteworthy enumerable classes.
Enumerable was covered briefly in
Enumerable Objects. This section provides more
detailed coverage.
Note that some enumerable classes have a natural enumeration
order that their each method
follows. Arrays, for example, enumerate their elements in order of
increasing array index. Range
enumerates in ascending order. And IO objects enumerate lines of text in the
order in which they are read from the underlying file or socket. In
Ruby 1.9, Hash and Set (which is based on Hash) enumerate their elements in the order
in which they were inserted. Prior to Ruby 1.9, however, these classes enumerate their
elements in what is essentially an arbitrary order.
Many Enumerable methods
return a processed version of the enumerable collection or a selected
subcollection of its elements. Usually, if an Enumerable method returns a collection (rather ...
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