Programming Ruby 2nd 读书笔记2

C05 Standard Types

1. String

 

print <<STRING1,<<STRING2
  Concat
  STRING1
    enate
    STRING2
produces:
  Concat
    enate

 

 

2. Range   

a = 1..3 #a = 1,2,3
a = 1...3 # a = 1,2

 

(1..10) === 5 ! true
(1..10) === 15 ! false
(1..10) === 3.14159 ! true
('a'..'j') === 'c' ! true
('a'..'j') === 'z' ! false

 

  
class UV
  include Comparable
  attr :volume
  def initialize(volume) # 0..9
    @volume = volume
  end
  def inspect
    '#' * @volume
  end
  # Support for ranges
  def <=>(other)
    self.volume <=> other.volume
  end
  def succ
    raise(IndexError, "Volume too big") if @volume >= 9
    VU.new(@volume.succ)
  end
end

 

(1..10) === 15 -> false
(1..10) === 3.14159 -> true
('a'..'j') === 'c' -> true
('a'..'j') === 'z' -> false

3. Regular Expression

re = /(\d+):(\d+)/ # match a time hh:mm
md = re.match("Time: 12:34am")
md.class -> MatchData
md[0] # == $& -> "12:34"
md[1] # == $1 -> "12"
md[2] # == $2 -> "34"
md.pre_match # == $` -> "Time: "
md.post_match # == $' -> "am"

 

C06 Method

1. 可变参数

 

def varargs(arg1, *rest)
  "Got #{arg1} and #{rest.join(', ')}"
end

puts(varargs("one", "two", "three"))

 

 

2.  Block

def take_block(p1)
  if block_given?
    yield(p1)
  else
    p1
  end
end

puts(take_block("no block"))
puts(take_block("no block"){|x| x.sub(/no /, '')})

class TaxCalculator
  def initialize(name, &block)
    @name = name
    @block = block
  end
  
  def get_tax(amount)
    "#{@name} on #{@amount} = #{@block.call(amount)}"
  end
end

tc = TaxCalculator.new("Sales Tax"){|amt| amt * 0.075}
puts(tc.get_tax(100))      

 

3.  Hash参数

def match_score(time, scores)
  puts("Match score on #{time}")
  scores.each do |name, score|
    puts("#{name} -- #{score}")
  end
end   

match_score('2009-03-15', 
           'Zhibin' => 7,
           'Henry' => 3,
           'Keyu' => 2
           )         

 

4.  Lambda

print('(t)imes or (p)lus')
times = gets
print('number:')
number = Integer(gets)
if times =~ /^t/
  calc = lambda { |n| n * number }
else
  calc = lambda { |n| n + number }
end
puts((1..10).collect(&calc).join(', '))  

 

C07 Expressions 

1.  Overload operator

 

class Fixnum
  alias old_plus +      
  
  def +(other)
    old_plus(other).succ
  end  
end
puts(1+2)        

 

2.  执行命令

puts(`date`)
puts($?)
puts(%x{echo 'hello world'})
puts($?) 
puts(`./test.x`) 
puts($?)     

 

3.  并行赋值

 

b, (c, d), e = 1,2,3,4 -> b == 1, c == 2, d == nil, e == 3
b, (c, d), e = [1,2,3,4] -> b == 1, c == 2, d == nil, e == 3
b, (c, d), e = 1,[2,3],4 -> b == 1, c == 2, d == 3, e == 4
b, (c, d), e = 1,[2,3,4],5 -> b == 1, c == 2, d == 3, e == 5
b, (c,*d), e = 1,[2,3,4],5 -> b == 1, c == 2, d == [3, 4], e == 5

4.  Case

 

def vowel_count(word)
  count = 0
  word.each_char do |c|
    case c
    when 'a'
      count += 1
    when 'e'   
      count += 1 
    when 'i'
      count += 1 
    when 'o'     
      count += 1 
    when 'u'
      count += 1 
    end
  end
  count  
end

puts(vowel_count('I love u!'))  

 

5. Variable Scope

while, for, if, util 这些都不会带来新的作用域，可是block的使用，会带来新的作用域。