详解Ruby中的代码块及其参数传递

(1..4).each{|v| print "#{v} "} #输出1 2 3 4 

sum = 0 
(1..5).each do |v| 
  name = 'smile' #name属于块内变量
  sum += v 
end 
p sum   #输出15，sum已改变
p name  #Error! name不可访问

name = 'outside' 
sum = 0 
(1..5).each do |v;name| #分号之后的name是块内变量
  name = 'inside' 
  sum += v 
end 
p sum   #输出15
p name  #输出outside，外部没被改变

def threeTime 
  yield 
  yield 
  yield 
end 
threeTime{p 'Hello world!'}  # 输出三行 Hello world!

def takeBlock(p1) 
 if block_given?   # 判断是否有块
  yield(p1) 
 else 
  p1 
 end 
end

takeBlock("no block")                    # 输出"no block"
takeBlock("no block") { |s| s.sub(/no /, '') } # 输出"block"

def nTime 
 i = yield   # 第一次调用获取块返回值
 (0..i).each {|v| yield(v)} 
end 
nTime do |v| 
 print "#{v} " if v 
 9   # 这个9就是yield的返回值
end 
# 输出 1 2 3 4 5 6 7 8 9

def nTime(n) 
 (0..n).each {|v| yield(v)} 
end 
nTime(9) do |v| 
 print "#{v} " 
end

class Array 
 def find 
  for i in 0...size 
   value = self[i] 
   return value if yield(value) 
  end 
  return nil 
 end 
end 
[1, 3, 5, 7, 9].find {|v| v > 5 } # 返回第一个大于5的数，即7

def fun   # 不带参数
 yield 
end 
proc = ->{p 'haha'} 
fun &proc

def fun2(x) # 带参数
 yield x 
end 
proc2 = ->(x){p x} 
fun2 1, &proc2

class MyClass 
 def initialize 
  @v = 1; 
 end 
end 
obj = MyClass.new 
obj.instance_eval do 
 puts self       # => # 
 puts @v        # => 1 
end 
obj.instance_exec(5) { |x| puts x * @v } # => 5