Download Ruby Language

Introduction to Ruby
张翼
[email protected]
Friday, May 17, 13
Your Attention Please!
This is a highly
condensed
presentation/course
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Origination
• Was first designed and
developed in the
mid-1990s by Yukihiro
Matsumoto (松本行弘 (まつ
もとゆきひろ) a.k.a. Matz in
Japan
• Got ideas from Perl,
Lisp, Small talk, and etc.
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Authoritative Resource
• ruby-lang.org
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Design Principles
• Focus on human factors
• Principle of Least Surprise
• Principle of Succinctness
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Principle of Least
Surprise
This principle is the supreme design goal of Ruby. It makes programers happy and makes ruby easy to
learn.
Examples:
1. What class is an object?
o.class
2. Is it Array#size of Array#length?
Either of the methods works. They re aliased
3. What are the different between arrays?
diff = ary1 - ary2
union = ary1 + ary2
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Principle of
Succinctness
A.K.A. Principle of Least Effort
• We don’t like to waste time on unnecessary
code (xml config files, getters, setters, etc)
• The quicker we program, the more we
accomplish
• Less code means less bugs
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Main features
• Everything is an object
• Dynamic typing and Duck typing
• Block
• Reflective
• Expressive
• ...
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irb - interactive ruby
shell
$ irb
irb(main):001:0> puts "Hello, World"
Hello, World
=> nil
irb(main):002:0> 1+2
=> 3
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Some fundamental
datatypes
• String
• Symbol
• Array
• Hash
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String
‘This is a simple Ruby string literal’
‘Won\’t you read O\‘Reilly\’s book?’
“\t\”This quote begins with a tab and ends with a
newline\”\n”
greeting = “Hello”
“#{greeting} World!”
“Hi “ * 3
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# => “Hello World!”
# => “Hi Hi Hi”
Symbol
:symbol
:”symbol”
:‘another long symbol’
str = “string”
sym = str.to_sym
str = sym.to_s
Two strings may hold the same content and yet be completely distinct
objects.
But two strings with the same content will both convert to exactly the
same Symbol object.
Two distinct Symbol objects will always have different content.
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Array
a = [1, 'hi', 3.14, 1, 2, [4, 5]]
puts
puts
puts
puts
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a[2]
a.[](2)
a.reverse
a.flatten.uniq
#
#
#
#
3.14
3.14
[[4, 5], 2, 1, 3.14, 'hi', 1]
[1, 'hi', 3.14, 2, 4, 5]
Hash
hash = Hash.new
hash = { :water => 'wet', :fire => 'hot' }
puts hash[:fire] # Prints: hot
hash.each_pair do |key, value| # Or:
puts "#{key} is #{value}"
end
# Prints:
#
hash.each do |key, value|
water is wet
fire is hot
hash.delete :water # Deletes water: 'wet'
hash.delete_if {|key,value| value=='hot'} # Deletes :fire => 'hot'
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Classes
class Person
attr_reader :name, :age
def initialize(name, age)
@name, @age = name, age
end
def <=>(person) # Comparison operator for sorting
age <=> person.age
end
def to_s
"#{name} (#{age})"
end
end
group = [
Person.new("Bob", 33),
Person.new("Chris", 16),
Person.new("Ash", 23)
]
puts group.sort.reverse
# => Bob (33)
# => Ash (23)
# => Chris (16)
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Open classes
class Person
def <=>(person)
name <=> person.name
end
end
puts group.sort.reverse
# => Chris (16)
# => Bob (33)
# => Ash (23)
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Blocks and iterators (1)
• Two syntaxes for creating a code block
{ puts “Hello World!” }
# or
begin
puts “Hello World!”
end
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Blocks and iterators (2)
3.times { puts “thank you!” }
data.each {|x| puts x}
[1,2,3].map {|x| x*x }
factorial = 1
2.upto(n) {|x| factorial *= x}
In Ruby we use the term iterator to mean any method that uses the yield statement.
They do not actually have to serve an iteration or looping function.
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Blocks and iterators (3)
Yielding the flow of program control to a block which was provided at
calling time:
def use_hello
yield "hello"
end
# Invoke the above method, passing it a block.
use_hello {|string| puts string} # => 'hello'
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Blocks and iterators (4)
A bit more complicated example:
def reduce(array)
if array.empty?
nil
else
result = array.shift
array.each do |item|
result = yield result, item
end
result
end
end
puts reduce([1, 2, 3, 4, 5]) {|a, b| a + b
puts reduce([1, 2, 3, 4, 5]) {|a, b| a * b
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}
}
# => 15
# => 120
Duck typing
class Duck
def quack
puts "Quaaaaaack!"
end
def feathers
puts "The duck has white and gray feathers."
end
end
class Person
def quack
puts "The person imitates a duck."
end
def feathers
puts "The person takes a feather from the ground and shows it."
end
end
def in_the_forest(duck)
duck.quack
duck.feathers
end
def game
donald = Duck.new
john = Person.new
in_the_forest donald
in_the_forest john
end
game
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Metaprogramming
COLORS = { black:
red:
green:
yellow:
blue:
magenta:
cyan:
white:
"000",
"f00",
"0f0",
"ff0",
"00f",
"f0f",
"0ff",
"fff" }
class String
COLORS.each do |color,code|
define_method "in_#{color}" do
"<span style=\"color: ##{code}\">#{self}</span>"
end
end
end
"Hello, World!".in_blue
==> "<span style==\"color: #00f\">Hello, World!</span>"
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Method Missing
class AttributeObject
def initialize
@attributes = {}
end
def method_missing(method, *args)
str_method = method.to_s
if str_method =~ /\=$/
str_method = str_method.sub(/\=$/, '')
@attributes[str_method.to_sym] = args[0]
else
@attributes[method]
end
end
end
john = AttributeObject.new
john.name = ‘John Conner’
john.age = 35
john.title = ‘UI designer’
puts john.name
puts john.age
puts john.title
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# => ‘John Conner’
# => 35
# => ‘UI designer’
Q &A
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