a simple cheatsheet for ruby

cheat_ruby.rb

# constants
MYCONSTANT = 123

# strings
myString = 'a b c'
myString = "a b c #{expression}'

# lists
myList = [1,2,3,4,5]
# some methods of list:
['select','map','each']

# hash/dictionary/associative-array
myHash = {myKey => myValue, ...}
myHash = {mySymbol: myObject, ...} # shortcut for {:mySymbol => myObject}

# a function/procedure (arg parens optional) (myaArg2=100 indicates default)
def myFn myArg1,myArg2=100
  return myArg1 * myArg2
end

# a code block
{|x| x**2}}
do |x| x**2 end

# lambdas and procs
myProc=lambda {|y| y**2}
# almost the same (no param count check; if it has a
# 'return' it will trigger a return in the calling context)
myProc=Proc.new {|y| y**2}
# call it
myProc.call
# use it in place of a code block
[my_list].select &myProc


# classes ("< MyParentClass" is optional)
# nb: "private" on a line by itself marks subsequent methods private (default
# is public, and there is a corresponding "public" indicator)
class MyClass < MyParentClass
  $myGlobalVar = 5
  @@myClassVar = 6
  attr_reader :myVar
  attr_writer :myOtherVar
  attr_accessor :myThirdVar
  def MyClass.myClassMethod
    return @@myClassVar
  end
  def initialize myArg
    @myInstanceVar = myArg
  end
  def myInstanceMethod
    super myArg2,myarg3...
    puts "myInstanceVar = #{@myInstanceVar}"
  end
end
myObj = MyClass.new("zork")
myObj.description

# Modules
module MyModule
  MYMODCONSTANT = 12345
end
MyModule::MYMODCONSTANT # scope designator

# Require and Include and Extend
require 'date' # can now use Date.today
include Math # can now use cos()
extend # like 'include' but at the class level
#
module Foo ; end
class Fah
  include Foo
end # Fah now has access to methods of Foo

# wtf?
numbers_array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
strings_array = numbers_array.collect &:to_s
#
String.new # okay
Integer.new # error
#
i=5 # equals sign, no type
class person {} # no equals, yes type
#
public/private markers in class definitions.