Merge pull request #18 from davefp/ruby

Ruby

ruby.html.markdown

@@ -0,0 +1,306 @@
+---
+language: ruby
+contributors:
+  - ["David Underwood", "http://theflyingdeveloper.com"]
+---
+
+```ruby
+# This is a comment
+
+=begin
+This is a multiline comment
+No-one uses them
+You shouldn't either
+=end
+
+# First and foremost: Everything is an object.
+
+# Numbers are objects
+
+3.class #=> Fixnum
+
+3.to_s #=> "3"
+
+
+# Some basic arithmetic
+1 + 1 #=> 2
+8 - 1 #=> 7
+10 * 2 #=> 20
+35 / 5 #=> 7
+
+# Special values are objects
+nil # Nothing to see here
+true # truth
+false # falsehood
+
+nil.class #=> NilClass
+true.class #=> TrueClass
+false.class #=> FalseClass
+
+# Equality
+1 == 1 #=> true
+2 == 1 #=> false
+
+# apart from false itself, nil is the only other 'falsey' value
+
+nil == false #=> true
+0 == false #=> false
+
+# Inequality
+1 != 1 #=> false
+2 != 1 #=> true
+!true  #=> false
+!false #=> true
+
+# More comparisons
+1 < 10 #=> true
+1 > 10 #=> false
+2 <= 2 #=> true
+2 >= 2 #=> true
+
+# Strings are objects
+
+'I am a string'.class #=> String
+"I am a string too".class #=> String
+
+placeholder = "use string interpolation"
+"I can #{placeholder} when using double quoted strings"
+#=> "I can use string interpolation when using double quoted strings"
+
+
+# print to the output
+puts "I'm printing!"
+
+# Variables
+x = 25 #=> 25
+x #=> 25
+
+# Note that assignment returns the value assigned
+# This means you can do multiple assignment:
+
+x = y = 10 #=> 10
+x #=> 10
+y #=> 10
+
+# By convention, use snake_case for variable names
+snake_case = true
+
+# Use descriptive variable names
+path_to_project_root = '/good/name/'
+path = '/bad/name/'
+
+# Symbols (are objects)
+# Symbols are immutable, reusable constants represented internally by an integer value
+# They're often used instead of strings to efficiently convey specific, meaningful values
+
+:pending.class #=> Symbol
+
+status = :pending
+
+status == :pending #=> true
+
+status == 'pending' #=> false
+
+status == :approved #=> false
+
+# Arrays
+
+# This is an array
+[1, 2, 3, 4, 5] #=> [1, 2, 3, 4, 5]
+
+# Arrays can contain different types of items
+
+array = [1, "hello", false] #=> => [1, "hello", false]
+
+# Arrays can be indexed
+# From the front
+array[0] #=> 1
+array[12] #=> nil
+
+# From the end
+array[-1] #=> 5
+
+# With a start and end index
+array[2, 4] #=> [3, 4, 5]
+
+# Or with a range
+array[1..3] #=> [2, 3, 4]
+
+# Add to an array like this
+array << 6 #=> [1, 2, 3, 4, 5, 6]
+
+# Hashes are Ruby's primary dictionary with keys/value pairs.
+# Hashes are denoted with curly braces:
+hash = {'color' => 'green', 'number' => 5}
+
+hash.keys #=> ['color', 'number']
+
+# Hashes can be quickly looked up by key:
+hash['color'] #=> 'green'
+hash['number'] #=> 5
+
+# Asking a hash for a key that doesn't exist returns nil:
+hash['nothing here'] #=> nil
+
+# Iterate over hashes with the #each method:
+hash.each do |k, v|
+  puts "#{k} is #{v}"
+end
+
+# Since Ruby 1.9, there's a special syntax when using symbols as keys:
+
+new_hash = { defcon: 3, action: true}
+
+new_hash.keys #=> [:defcon, :action]
+
+# Tip: Both Arrays and Hashes are Enumerable
+# This means they share a lot of useful methods such as each, map, count, and more
+
+# Control structures
+
+if true
+  "if statement"
+elsif false
+ "else if, optional"
+else
+ "else, also optional"
+end
+
+for counter in 1..5
+  puts "iteration #{counter}"
+end
+#=> iteration 1
+#=> iteration 2
+#=> iteration 3
+#=> iteration 4
+#=> iteration 5
+
+# HOWEVER
+# No-one uses for loops
+# Use `each` instead, like this:
+
+(1..5).each do |counter|
+  puts "iteration #{counter}"
+end
+#=> iteration 1
+#=> iteration 2
+#=> iteration 3
+#=> iteration 4
+#=> iteration 5
+
+counter = 1
+while counter <= 5 do
+  puts "iteration #{counter}"
+end
+#=> iteration 1
+#=> iteration 2
+#=> iteration 3
+#=> iteration 4
+#=> iteration 5
+
+grade = 'B'
+
+case grade
+when 'A'
+  puts "Way to go kiddo"
+when 'B'
+  puts "Better luck next time"
+when 'C'
+  puts "You can do better"
+when 'D'
+  puts "Scraping through"
+when 'F'
+  puts "You failed!"
+
+
+# Functions
+
+def double(x)
+  x * 2
+end
+
+# Functions (and all blocks) implcitly return the value of the last statement
+double(2) #=> 4
+
+# Parentheses are optional where the result is unambiguous
+double 3 #=> 6
+
+double double 3 #=> 12
+
+def sum(x,y)
+  x + y
+end
+
+# Method arguments are separated by a comma
+sum 3, 4 #=> 7
+
+sum sum(3,4), 5 #=> 12
+
+# yield
+# All methods have an implicit, optional block parameter
+# it can be called with the 'yield' keyword
+
+def surround
+  puts "{"
+  yield
+  puts "}"
+end
+
+surround { puts 'hello world' }
+
+# {
+# hello world
+# }
+
+
+# Define a class with the class keyword
+class Human
+
+     # A class variable. It is shared by all instances of this class.
+    @@species = "H. sapiens"
+
+    # Basic initializer
+    def initialize(name, age=0):
+        # Assign the argument to the "name" instance variable for the instance
+        @name = name
+        # If no age given, we will fall back to the default in the arguments list.
+        @age = age
+    end
+
+    # Basic setter method
+    def name=(name)
+        @name = name
+    end
+
+    # Basic getter method
+    def name
+        @name
+    end
+
+    # A class method; uses self to distinguish from instance methods. (Can only be called on class, not an instance).
+
+    def self.say(msg)
+       puts "#{msg}"
+    end
+
+    def species
+        @@species
+    end
+
+end
+
+
+# Instantiate a class
+jim = Human.new("Jim Halpert")
+
+dwight = Human.new("Dwight K. Schrute")
+
+# Let's call a couple of methods
+jim.species #=> "H. sapiens"
+jim.name #=> "Jim Halpert"
+dwight.species #=> "H. sapiens"
+dwight.name #=> "Dwight K. Schrute"
+
+# Call the class method
+Human.say("Hi") #=> "Hi"
+```