Given a class, you want an object corresponding to its class, or to the parent of its class.
Use the Object#class method to get the class of an object as a Class object. Use Class#superclass to get the parent Class of a Class object:
'a string'.class # => String 'a string'.class.name # => "String" 'a string'.class.superclass # => Object String.superclass # => Object String.class # => Class String.class.superclass # => Module 'a string'.class.new # => ""
Class objects in Ruby are first-class objects that can be assigned to variables, passed as arguments to methods, and modified dynamically. Many of the recipes in this chapter and Chapter 8 discuss things you can do with a Class object once you have it.
The superclass of the Object class is nil. This makes it easy to iterate up an inheritance hierarchy:
class Class def hierarchy (superclass ? superclass.hierarchy : ) << self end end Array.hierarchy # => [Object, Array] class MyArray < Array end MyArray.hierarchy # => [Object, Array, MyArray]
While Ruby does not support multiple inheritance, the language allows mixin Modules that simulate it (see Recipe 9.1). The Modules included by a given Class (or another Module) are accessible from the Module#ancestors method.
A class can have only one superclass, but it may have any number of ancestors. The list returned by Module#ancestors contains the entire inheritance hierarchy (including the class itself), any modules the class includes, and the ever-present Kernel module, whose methods are accessible from anywhere because Object itself mixes it in.
String.superclass # => Object String.ancestors # => [String, Enumerable, Comparable, Object, Kernel] Array.ancestors # => [Array, Enumerable, Object, Kernel] MyArray.ancestors # => [MyArray, Array, Enumerable, Object, Kernel] Object.ancestors # => [Object, Kernel] class MyClass end MyClass.ancestors # => [MyClass, Object, Kernel]
Date and Time
Files and Directories
Code Blocks and Iteration
Objects and Classes8
Modules and Namespaces
Reflection and Metaprogramming
XML and HTML
Graphics and Other File Formats
Databases and Persistence
Web Development Ruby on Rails
Web Services and Distributed Programming
Testing, Debugging, Optimizing, and Documenting
Packaging and Distributing Software
Automating Tasks with Rake
Multitasking and Multithreading
Extending Ruby with Other Languages