This document discusses strings and symbols in Ruby. It covers how to create, manipulate, and iterate over strings using various string methods. It also explains what symbols are, how they are different from strings, and why they are useful - namely that they are immutable and unique identifiers.

1. Class 3 Strings and Symbols

2. Strings “I am a string!”

3. Quoting Strings Double quotes interpolate >> name = ”Sam” >> "hello #{name}" => "hello Sam" Single quotes don’t interpolate >> 'hello #{name}' => "hello {name}"

4. Concatenating Strings first_name = ”Sam” last_name = ”Smith” full_name = first_name + " " + last_name => ”Sam Smith" full_name = first_name << " " << last_name => ”Sam Smith"

5. String Formatting: upcase >> full_name.upcase => ”SAM SMITH” >> full_name => ”Sam Smith" >> full_name.upcase! => ”SAM SMITH" >> full_name => ”SAM SMITH"

6. More String Formatting >> full_name.downcase! => ”sam smith" >> full_name.capitalize => ”Sam smith" Making our own title case method: >> full_name.split.map {|w| w.capitalize}.join(" ") => ”Sam Smith"

7. Access a String’s Characters >> full_name[2].chr => "m” >> full_name[0,1] => "S” >> full_name[2,4] => "m Sm" >> full_name[4..6] => "Smi"

8. Ruby 1.8 >> name = "Yukihiro” => "Yukihiro” >> name[4] => 104 >> name[4].chr => "h" >> name = "こんいちわ” =>"43012343022343010443014143021” >> name[2] => 147

9. Ruby 1.9 >> name = "yukihiro” => "yukihiro” >> name[4] => "h” >> name = "こんいちわ” => "こんいちわ” >> name[2] => "い” >> name[0] => "こ"

10. Modifying a String >> full_name.slice!("Sam") => "Sam" >> full_name => " Smith" >> full_name["Sam"] = "Fred" => "Fred" >> full_name => "Fred Smith" >> full_name[0,4] = "Greg" => "Greg" >> full_name => "Greg Smith"

11. Query a String >> full_name.include?(”Greg") => true >> full_name.empty? => false >> full_name.size => 10

13. Iterate Using Split returns an array of partial strings exploded at a separator secret_code = "the black dove flies at night” secret_code.split(" ").each do |s| puts s.reverse end eht kcalb evod seilf ta thgin

14. Symbols :i_am_a_symbol

15. What is a Symbol? A symbol represents a name. Instances of the built-in class Symbol. They efficiently describe names while saving the space one would use to generate a string for each naming instance.

16. A Symbol is not a String :thing != “thing” However a symbol can be create from a string: “thing”.to_sym And a string can be created from a symbol :thing.to_s

17. Symbols are Immutable You can’t change a symbol For example, you can’t append characters to a symbol...once a symbol exists, that’s it! >> :name + :me NoMethodError: undefined method `+' for :name:Symbol from (irb):182 from :0 >> :name << :me NoMethodError: undefined method `<<' for :name:Symbol from (irb):183 from :0

18. Symbols are Unique :name is the only symbol object called :name >> :name.object_id => 68828 >> :name.object_id => 68828 “name” is a new String object each time it is instantiated >> "name".object_id => 2157595700 >> "name".object_id => 2157591380