This document discusses Ruby method and constant lookup. It explains that modules are included into classes but not instantiated on their own. When a module is included, its methods are copied to the including class. Ruby uses a method lookup algorithm that searches from the including class up the inheritance hierarchy and included modules. Constant lookup uses lexical scope, searching from the current class/module outward. The document provides examples and use cases of module inclusion and method/constant lookup.

1. Rubymethod&constant
lookup

2. Index
1. Module
2. Ruby Method Lookup
3. Module use cases
4. Ruby Constant Lookup

3. Module
module BaseInfo
def title
end
def isbn
end
end

4. ModuleisnotClassinmanyways
/*WRONG*/
module BaseInfo
end
@base = BaseInfo.new
/*WRONG*/
module BaseInfo < Base
end
/*CORRECT*/
module BaseInfo
end
class ClassicNovel
include BaseInfo
end

5. IncludingModuleintoaClass
module BaseInfo
end
class ClassicNovel < Novel
include BaseInfo
end

6. Superclass linkedlist
ClassicNovel
Novel
Object
Included
class
BaseInfo
copy

7. RubyMethodLookupAlgorithm

8. Example
- 1 Class, 1 super class, 1 module
class Novel
attr_accessor :title
attr_accessor :category
end
module BaseInfo
def print
end
end
class ClassicNovel < Novel
include BaseInfo
end

9. Globalmethodcache
klass defined_class
Fixnum#times Integer#times
Object#puts BasicObject#puts

10. Multipleinheritance
Include multiple modules
module Status
end
module BaseInfo
def print
end
end
class ClassicNovel < Novel
include BaseInfo
include Status
end

11. Includeonemoduleintoanother
module Status
end
module BaseInfo
include Status
def print
end
end
class ClassicNovel < Novel
include BaseInfo
end

12. Usecase1:
- Need to use prepend? (available from ruby 2.0)

13. Howprependwork
Novel
Status
“Origin” Novel
Object
Move attr_accessor :title to
“Origin” Novel

14. Usecase2:
Modify a module after including?
Ruby copy structure of module, keep pointer to method table

15. Usecase3:
Include submodule into included module?

16. ConstantLookup
the same with method lookup?
- Using lexical scope
- Same algorithm

17. LexicalScope

18. ConstantLookupAlgorithm