ruby_intro.md

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Language	Framework

#   #  

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Matz (Yukihiro Matsumoto)

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####People want to express themselves when they program. ####  ####They don't want to fight with the language. ####  ####Programming languages must feel natural to programmers. ####  ####I tried to make people enjoy programming and concentrate on the fun and creative part of programming when they use Ruby.

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Ruby 1.0 released in 1996

open source

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Ruby Language Overview

• Dynamically typed
• Interpreted
• Can be modified at runtime
• Object oriented
• Blocks & lambdas
• Perl-like Regular Expressions

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Let's get started

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IRB: Interactive RuBy

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>> 4
>> 4 + 4

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Everything is an object

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“test”.upcase
“test”.class
“test”.methods

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Everything evaluates to something

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2 + 2
(2+2).zero?

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Methods are messages

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thing.do(4)
thing.do 4
thing.send "do", 4

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Operators are Methods

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1 + 2
1.+(2)
1.send "+", 2

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# is a comment

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Ruby aims to be elegant and readable

so punctuation and boilerplate are minimal

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You don't need semicolons

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Use parens when you need them

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>> "Hello".gsub 'H', 'h' 
=> "hello"

>> "Hello".gsub("H", "h").reverse 
=> "olleh"

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Variables, symbols, constants

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:this_is_a_symbol

There is only one representation of a given symbol in memory, so it really means "the thing named :this_is_a_symbol" to the ruby interpreter. In ruby, we prefer symbols over hardcoded globals or strings. They're very lightweight.

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Collections

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Arrays are sized dynamically and can be of mixed types.

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a = [1, 2, 3]
a.push "four" #=> [1, 2, 3, "four"]
a.pop #=> "four"
a[0] #=> 1

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Hashes are like an associative map

!SLIDE states = {"MA" => "Massachusetts", "CA" => "California"} states["MA"]

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my_hash = {:a_symbol => 3, "a string" => 4}
my_hash[:a_symbol] 
=> 3

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String interpolation

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"string #{ruby code} string"

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>> a = "world"   
>> puts "hello #{a}"
hello world
>> a = 2
>> puts "hello #{a}"
hello 2
>> a = nil
>> puts "hello #{a}"
hello 

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Iteration

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my_array = ["cat", "dog", ”world"]
my_array.each do |item|
  puts "hello " + item
end

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my_hash = { :type => "cat", 
            :name => "Beckett", 
            :breed => "alley cat" }
my_hash.each do |key, value|
  puts "My " + key.to_s + " is " + value
end

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Classes and methods

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class Thing
  def return_something
    "something"
  end
end

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class Thing
  def do_something(a,b)
    a + b 
  end
end

!SLIDE   var @var @@var $var VAR

!SLIDE   var # could be a local variable @var # instance variable @@var # class variable $var # global variable VAR # constant

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Methods can take blocks, which are like anonymous functions.

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my_array = ["cat", "dog", ”world"]
my_array.each do |item|
  puts "hello " + item
end

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def do_something yield end

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[1, 2, 3].each do |item|
   puts "#{item} is #{item.even? ? "even" : "odd"}."
end

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Blocks can also return a value. Map translates each item in an array.

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>> ["hello", "world"].map{ |string| string.upcase } 
=> ["HELLO", "WORLD"]

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more neat things about ruby

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duck typing

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def print_even_or_odd(array_like_thing)
  array_like_thing.each do |item|
    puts "#{item} is #{item.even? ? "even" : "odd"}."
  end
end

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print_even_or_odd [1, 2, 3]
print_even_or_odd 1..3

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advanced ruby

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meta-programming

creating Domain-Specific Languages (DSLs)

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#Rails #Rake #Cucumber #Rspec #etc

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method_missing

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private vs public

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####Private really just means "please don't come in." ####  ####If someone has access to your runtime environment, they are trusted. ####  ####Spend your time writing code (and testing it), not protecting yourself from other programmers.

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class Fixnum
  def even?
    self % 2 == 0
  end
end

1.even? #=> false

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everything is an object

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Classes are objects

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class methods are really just methods on the class object.

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Code evaluated in the scope of a class definition acts on the class object.

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Have fun!