Ruby symbols review: Learn Ruby The Hard Way

ex37.rb

descriptions = {}
# ========
# KEYWORDS
# ========


# -----
# alias
# -----

descriptions[:alias] = "Create a second name for the method or variable. See: http://ruby.about.com/od/rubyfeatures/a/aliasing.htm"

class Microwave
  def on
    puts "The microwave is on."
  end

  alias :start :on
end

def alias_example
  m = Microwave.new
  m.start # same as m.on
end


# and


# -----
# BEGIN
# -----

descriptions[:BEGIN] = "A preprocessor. Anywhere a BEGIN block is encountered during the initial scan/pass-through, it's automatically ran before the rest of the file is executed. Useful for stream processing. See: http://burkelibbey.posterous.com/rubys-other-begin"

puts :first
BEGIN { puts :second }
puts :third


# -----
# begin
# -----

descriptions[:begin] = "Exception handling purposes. See: http://stackoverflow.com/questions/2191632/begin-rescue-and-ensure-in-ruby"

# General flow of exception handling
begin
  # Something which might raise an exception.
rescue SomeExceptionClass => some_variable
  # Code that deals with some exception with the error message in
  # some_variable.
  #
  # If SomeExceptionClass is left out, all exceptions that inherit from
  # StandardError will be caught. Other exceptions include
  # SystemStackError, NoMemoryError, SecurityError, NotImplementedError,
  # LoadError, SyntaxError, ScriptError, Interrupt, SignalException and
  # SystemExit.
rescue SomeOtherExceptionClass => some_other_variable
  # Code that deals with some other exception with the error message in some_other_variable
else
  # Code that runs only if no exception is raised.
ensure
  # Code that must always run, no matter what.
end

# Function, class and module definitions are all implicit exception
# blocks.
def foo
  # ...
rescue
  # ...
end


# -----
# break
# -----

descriptions[:break] = "Terminates the most inner loop, or terminates a method with an associated block if called within the block."

for i in 0..5
  if i > 2 then
    break
  end
  puts "Value of i is #{i}."
end


# ----
# case
# ----

descriptions[:case] = "Test a sequence of conditions, similar to switch in C and Java."

i = 8
case i
when 1, 2..5
  puts "1..5"
when 6..10
  puts "6..10"
end

case 'abcdef'
when 'aaa', 'bbb'
  puts "aaa or bbb"
when /def/ # Regular expression compatible
  puts "includes /def/"
end

# class
# def
# defined?


# --
# do
# --

descriptions[:do] = "Block delimiter. Opens a code block."

collection.select do |x|
  # ...
  puts x
  # ...
end


# else
# elsif


# ---
# END
# ---

descriptions[:END] = "Post-processor, opposite of BEGIN. See: http://burkelibbey.posterous.com/rubys-other-begin"


# ---
# end
# ---

descriptions[:end] = "Block delimiter. Closes a code block."


# ------
# ensure
# ------

descriptions[:ensure] = "See: begin"


# false
# for
# if
# in

# ------
# module
# ------

descriptions[:module] = "Modules are similar to classes, except that they have no instances or subclasses."

require Math

# Module method
x = Math.sqrt(2)

# Module constant
pi_value = Math::PI

# next
# nil
# not
# or
# redo

# ------
# rescue
# ------

descriptions[:rescue] = "See: begin"


# retry
# return
# self
# super
# then
# true
# undef
# unless

# -----
# until
# -----

descriptions[:until] = "Opposite of while. Execute when the conditional is false."

i = 0
until i > 5 do
  i += 1
  puts "The value of i is #{i}"
end


# ----
# when
# ----

descriptions[:when] = "See: case"

# while
# yield


#DATA TYPES
#==========

# true
# false
# nil
# constants
# strings
# numbers
# ranges


# ------
# arrays
# ------

a = [3.14159, "pie", 99]
a.type # Array
a.length # 3
a[-2, 2] # ["pie", 99]
a[1..2] # [3.14159, "pie"]
b = Array.new
b.type # Array
b[0] = "first"
b[1] = "second"
b # ["first", "second"]


# hashes


#STRING ESCAPE SEQUENCES
#=======================

# \\
# \'
# \"
# \a
# \b
# \f
# \n
# \r
# \t
# \v


#OPERATORS
#=========

# ::
# []
# **
# -(unary)
# +(unary)
# !
# ~
# *
# /
# %
# +
# -
# <<
# >>
# &
# |
# >
# >=
# <
# <=
# <=>
# ==
# ===
# !=
# =~
# !~
# &&
# ||
# ..
# ...