Enumerable is a module that provides common iteration methods for collections like Array and Hash. It defines methods like collect, find, select, and grep that allow you to iterate through elements and return new collections. To use Enumerable, a class must include the module and define an each method to iterate over its elements. This allows the iteration methods to work uniformly across different data types.

1. Inside Enumerable Mike Bowler Gargoyle Software Inc.

2. Agenda What is Enumerable? What can you do with it? How does it do that?

3. What is it? It’s a group of related methods all having to do with collections It’s the interesting part behind Array, Set, Hash and Range It’s a Module (often called a mixin)

4. hash = { :a => 1, :b => 2} hash.collect do |key, value| value * 4 end [4,8] [4,8,12] [4,8,12] array = [1,2,3] array.collect do |value| value * 4 end range = 1..3 range.collect do |value| value * 4 end

5. hash = { :a => 1, :b => 2} hash.collect do |key, value| value * 4 end array = [1,2,3] array.collect do |value| value * 4 end range = 1..3 range.collect do |value| value * 4 end module Enumerable def collect ... end end

6. multiple inheritance

7. mixins

8. Mixins Cannot be instantiated Can be mixed in

9. Mixins usually don’t stand alone don’t stand alone Typically... mixins aren’t completely self-contained they rely on certain methods being present on the class they are mixed into This isn’t mandatory but is very common Let’s look at an example...

10. Enumerable requires each() [1,2,3].collect {|i| i*2} [2,4,6]

11. Enumerable.collect class Foo include Enumerable def each yield 1 yield 2 yield 3 end end Foo.new.collect do |num| num * 2 end module Enumerable def collect array = [] each do |a| array << yield (a) end array end end

12. Enumerable.collect module Enumerable def collect array = [] each do |a| array << yield (a) end array end end class Foo include Enumerable def each yield 1 yield 2 yield 3 end end Foo.new.collect do |num| num * 2 end

13. Enumerable.collect module Enumerable def collect array = [] each do |a| array << yield (a) end array end end class Foo include Enumerable def each yield 1 yield 2 yield 3 end end Foo.new.collect do |num| num * 2 end

14. Enumerable.collect class Foo include Enumerable def each yield 1 yield 2 yield 3 end end Foo.new.collect do |num| num * 2 end module Enumerable def collect array = [] each do |a| array << yield (a) end array end end

15. Enumerable.collect module Enumerable def collect array = [] each do |a| array << yield (a) end array end end class Foo include Enumerable def each yield 1 yield 2 yield 3 end end Foo.new.collect do |num| num * 2 end

16. Enumerable.collect class Foo include Enumerable def each yield 1 yield 2 yield 3 end end Foo.new.collect do |num| num * 2 end module Enumerable def collect array = [] each do |a| array << yield (a) end array end end Result [2,4,6]

17. Required methods collect() would not have worked if Foo hadn’t declared each() All methods in Enumerable require each() A couple also require <=> min(), max(), sort() Comparison operator

18. Enumerable methods all?, any?, collect, detect, each_cons, each_slice, each_with_index, entries, enum_cons, enum_slice, enum_with_index, find, find_all, grep, include?, inject, map, max, member?, min, partition, reject, select, sort, sort_by, to_a, to_set, zip

19. any? [1,2,3,4].any? {|a| a > 2} Returns true if this block... ...returns true for any of these values

20. all? [1,2,3,4].all? {|a| a > 2} Returns true if this block... ...returns true for ALL of these values

21. collect, map “Returns a new array with the results of running block once for every element in enum” map is an alias for collect [1,2,3].collect {|i| i*2} [2,4,6]

22. find, detect find(ifnone = nil) {| obj | block } => obj or nil Passes each entry in enum to block. Returns the first for which block is not false. If no object matches, calls ifnone and returns its result when it is specified, or returns nil detect is an alias for find

23. find_all, select find_all {| obj | block } => array Returns an array containing all elements of enum for which block is not false select is an alias for find_all

24. grep grep(pattern) => array Returns an array of every element in enum for which Pattern === element. If the optional block is supplied, each matching element is passed to it, and the block‘s result is stored in the output array Case equality

25. Case equality For most objects, === is the same as == Case equality Regular equality

26. Case equality case myvar when 1..50 # do something when 51 # do something when /^\d+$/ # do something end Within the range This exact number Matches this regular expression Different kind of equality as a convenience in case statements

27. Case equality in grep [1,2,3].grep(1..50) [1,2,3].grep(51) [1,2,3].grep(/^\d+$/) Within the range This exact number Matches this regular expression

28. Wrap up Enumerable is already mixed into all the core collections You can mix it into any of your classes so long as you implement each() It provides all kinds of useful methods to walk across the collections and get information out of them

29. Shameless Plug I can help you with your Ruby and/or Rails projects. Ask me how. Mike Bowler [email_address] www.GargoyleSoftware.com (company) www.SphericalImprovement.com (blog)