In our third session we covered the second half of our language crash course. This session addresses Arrays, Hashes, Symbols, Control Structures, Regular Expressions, Blocks and Iterators.

1. Learn Ruby 2011
Session 3

2. Our Sponsors
Flatsourcing, iSeatz, Koda, and Launchpad

3. Language Crashing
Learning the basics in pieces

4. Questions
Having any problems? Discover anything cool?

5. Arrays
• An Array is an ordered list of values
• Arrays in Ruby are zero-indexed

6. Arrays
array = [“One”,”Two”,”Three”]
puts array[0]
One
array.each { |v| puts v }
One
Two
Three

7. Hashes
• Hashes are unordered lists of values
• Hashes are indexed using “keys” which can
being either strings or symbols

8. Hashes
hash = {‘one’ => “One”, :two => ”Two”}
puts hash[‘one’]
One
puts hash[:two]
Three

9. Symbols
• Symbols are essentially constants that don’t
need to be declared ahead of time
• A Symbol has a simple string-like
representation and is guaranteed to have a
unique value

10. Symbols
def walk(direction)
if direction == :north
# ...
end
end

11. Symbols
• Symbols are most commonly found as the
keys for hashes
• They are slightly more memory efficient than
using strings for the same purposes

12. Control Structures
• Control structures allow you to handle
conditional behaviors
• Control structures allow you to handle
iterations/loops

13. Control Structures
• if ... else ... elsif
• while
• case ... when
• for ... in
• until
• unless

14. Control Structures
if i == 3
# ...
elsif i == 4
# ...
else
# ...
end

15. Control Structures
unless i == 3
# ...
end

16. Control Structures
while i < 3
# ...
end

17. Control Structures
until i < 3
# ...
end

18. Control Structures
case i
when 3
# ...
when 4
# ...
else
# ...
end

19. Control Structures
for i in 1..3
# ...
end
for i in [‘one’,‘two’,‘three’]
# ...
end

20. Regular Expressions
• Regular Expressions are used for text parsing
and manipulation
• They can represent a sort of programming
language unto themselves

21. Blocks
• Sections of code that can be passed to
methods like parameters
• Represented as code within curly braces or
between do and end

22. Blocks
def call_block
puts "Start of method"
yield
puts "End of method"
end
call_block { puts "In the block" }
Start of method
In the block
End of method

23. Iterators
• A type of code block that works with
successive values of some collection
• Used extensively for arrays and hashes

24. Iterators
[‘One’,‘Two’,‘Three’].each do |val|
puts val
end
One
Two
Three

25. Reviewing
• Arrays & Hashes
• Symbols
• Control Structures
• Regular Expressions
• Blocks & Iterators

26. For Next Week
For the New to Programming
• Read Chapters 5, 6, 7 & 8 in LtP
• Complete exercises for each chapter
For Everyone
• Read Chapter 2, 7 & 9 in PR1.9
• Work on the Ruby Koans at a leisurely
pace

27. Next Week
• Deeper into Classes & Variables

28. Exercises
• Visit http://rubykoans.com/ & Download
• Begin working through the Koans by
running `ruby path_to_enlightenment.rb`
•