I bought it three months ago, but never read it once since then. It is a Chinese-translated edition, because the original book is written in Japanese, which I am totally not familiar with, not even a word. I gonna to read it, write some notes and hope finish this book in not very long time.

Basics

“Hello World” is always a best friend of novice.
I am going to begin my journey of ruby with its basic output functions.

Standard outputs

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=begin
ruby style's multi-line comments.
=end

print("Hello World\n"); #=> Hello World
# note: semicolon is not nesessary. ruby is not JAVA

puts('Hello World') #=> Hello World
# Same as above except "\n" is automatically added at the end of string.

p('Hello World') #=> 'Hello World'
# "p()" is simply output data in its natrual literal form.

Standard outputs revisited

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a = 'World'

print("Hello ", a, "\n")
print("Hello #{a}\n")
puts("Hello #{a}")
#=> Hello World
# Three of above have no differences.

Loops

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(10.times do |i|
    print(i)
end).times do
    print(i)
end
#=> 01234567890123456789

What?
Yes, that’s a use of chain rule, as times is a function that return itself, which is 10. 10 is a instance of Fixnum , which is also a subclass of Integer. Let’s take look at the big picture of Numeric class hiearchy in Ruby.¹

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Numeric
    -> Integer            #-> method "times" lies in.
        -> Fixnum         #-> where 10 comes from.
        -> Bignum

Everything is object

That’s ruby, everything is object. Unlike java, there is no primitive type. You might wondering where print() comes from². IO is where it comes from. There are three constant, STDIN, STDOUT and STDERR, which is pointed by ruby’s global variables, $stdin, $stdout and $sterr respectively.
print() is a alias of $stdout.print() provided by ruby’s Kernel module.

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$stdout.print('I am a alias')
# is equivelent to
print('I am a alias')

Array and Hash

Beside String and Numeric two basic structure, Ruby has two more advanced data structure - Array and Hash. You can think of both as Java’s Listand Map.

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names = ['sabonis', 'sprewell', 'shiren']
#=> ['sabonis', 'sprewell', 'shiren']

mix = ['sabonis', 29]
#=> Ruby supports different types in one container.

# Size of array
names.size()
#=> 3

# Iteration
names.each { |item|
    print(item, '')
}
#=> sabonis sprewell shiren
# {...} is same as "do ... end" block.

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address = {:city => 'Taipei', :country => 'Taiwan'}

# Iteration
address.each {|key, value|
    puts(key, ' => ', value)
}
#=> city => Taipei
#=> country => Taiwan

:city is a Symbol of ruby, you can think of this as a lightweight version of String.

The same Symbol object will be created for a given name or string for the duration of a program's execution, regardless of the context or meaning of that name.

Per doc says, there will be one instance of Symbol with same name till program ended.

Notes