1. John Pinney j.pinney@imperial.ac.uk
Ruby in 20 minutes
John Pinney

2. What is Ruby?
A true object-oriented language with easily understandable syntax and convenient notations. => pure / elegant / powerful “I wanted a scripting language that was more powerful than Perl, and more object-oriented than Python.” Yukihiro Matsumoto (“Matz”)

3. The Ruby interpreter
> irb puts "Hello World" Hello World

4. (Almost) everything is an object
There are no primitives in Ruby.
Nearly everything can be considered as an object, i.e.
is an instance of a class
has an interface for method invocation

5. "hello". reverse => "olleh” 44. even. => true nil
"hello".reverse => "olleh” 44.even? => true nil.class => NilClass nil.class.class => Class

6. Parts of speech
Variables Numbers Strings Symbols Constants Ranges Regular Expressions
Methods + arguments
Blocks + arguments
Arrays
Hashes
Operators
Keywords

7. Variables
local_variable = = 4.6 = 8.9 = “attribute”) $global_variable = 2.5

8. Numbers
1.class => Fixnum 1.0.class => Float

9. Symbols Symbols (starting with a colon ) are like lightweight strings.
They always point to the same object, wherever used in the code.
x = :my_symbol

10. Methods front_door.open front_door.open.close front_door.is_open?
front_door.paint(3,:red)
front_door.paint(3,:red).dry(30).close

11. Kernel methods are invoked by their names alone.
This is just a bit of syntactic sugar.
print "Hello\n"
Hello
Kernel.print("Hello\n")
(print is really a class method of Kernel)

12. Operators Operators behave as you would expect: 1 + 2 3
But in Ruby they are actually methods!
1.+(2)
Since all operators are methods, they can be defined as you like for your own classes, or even re-defined for existing classes.

13. Blocks
Any code surrounded by curly braces is a closure, known as a block:
20.times{
print 'CAG' }
CAGCAGCAGCAGCAGCAGCAGCAGCAGCAGCAGCAGCAGCAGCAGCAGCAGCAGCAGCAG
Blocks are sets of instructions that can be passed around the program.

14. Blocks can also take arguments, delimited by pipe characters:
"Hello".each_char{|ch| puts ch} H e l o

15. Braces can be replaced by the keywords do and end.
"Hello".each_char do |ch|
puts ch
end H e l o

16. Effective use of blocks can allow highly transparent code:
a = [ "a", "b", "c", "d" ]
a.collect { |x| x + "!" }
["a!", "b!", "c!", "d!"]

17. Regular expressions
Regex is very simple to use in Ruby (much nicer than Python!)
text = "Cats are smarter than dogs”;
if ( text =~ /(C|c)at(.*)/ ) then
puts "I found a cat"
end
I found a cat

18. Example class Greeter def initialize(name = "World") @name = name end
def say_hi
puts "Hi
def say_bye
puts "Bye come back soon."

19. g = Greeter. new("Pat") g. say_hi Hi Pat. g
g = Greeter.new("Pat") g.say_hi Hi Pat! g.say_bye Bye Pat, come back soon. g.name NoMethodError: undefined method 'name' for

20. class Greeter attr_accessor :name end g. name => "Pat" g
class Greeter attr_accessor :name end g.name => "Pat" g.name = "John" g.say_hi Hi John!

21. Sources: https://www. ruby-lang