Ruby中迭代器Iterator的使用教程

　　今天小编给大家分享一篇ruby.html" target="_blank">Ruby中迭代器Iterator的使用教程，感兴趣的朋友跟小编一起来了解一下吧!

　　Iterator 定义

　　A Ruby iterator is simple a method that can invoke a block of code.

　　Block 一般是跟着 method 出现的, 并且 block 中的代码不一定会执行

　　如果 method 中有 yield, 那么它的block 中的代码会被执行

　　Block 可以接收参数，和返回 value

　　def two_times

　　yield

　　yield

　　end

　　two_times { puts "Hello" }

　　# Hello

　　# Hello

　　def fib_up_to(max)

　　i1, i2 = 1. 1

　　while i1

　　yield i1

　　i1, i2 = i2, i1 + i2

　　end

　　end

　　fib_up_to(1000) { |f| print f, " " }

　　# 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987

　　上面代码中的 yield 之后的 i1 会作为 parameter 传入到 block 中， 赋值给 block 的 argument f。

　　Block 中可以有多个 arguments.

　　常见的 iterator each

　　each is probable the simplest iterator - all it does is yield successive elements of its collection.

　　[1, 3, 5, 7, 9].each { |i| puts i }

　　# 1

　　# 3

　　# 5

　　# 7

　　# 9

　　find

　　A blocl may also return a value to the method. The value of the last expression evaluated in the block is passed back to the method as the value of the yield.

　　class Array

　　def find

　　each do |value|

　　return value if yield(value)

　　end

　　end

　　end

　　[1,3,4,7,9].find { |v| V*V > 30 } # => 7

　　collect (also known as map)

　　Which takes each element from the collection and passes it to the block. The results returned by the block are used to construct a new array

　　["H", "A", "L"].collect { |x| x.succ } # => ["I", "B", "M"]

　　inject

　　The inject method lets you accumulate a value across the members of a collection.

　　[1,3,5,7].inject { |sum, element| sum + element } # => 16

　　# sum = 1, element = 3

　　# sum = 4, element = 5

　　# sum = 9, element = 7

　　# sum = 16

　　[1,3,5,6].inject { |product, element| product*element } # => 105

　　If inject is called with no parameter, it uses the first element of the collections as the initial value and starts the iteration with the second value.

　　上面代码的另一种简便写法：

　　[1,3,5,7].inject(:+) # => 16

　　[1,3,5,7]/inject(:*) # => 105

　　Iterator 和 I/O 系统的交互

　　Iterators 不仅仅能够访问 Array 和 Hash 中的数据， 和可以和 I/O 系统交互

　　f = File.open("testfile")

　　f.each do |line|

　　puts "The line is: #{line}"

　　end

　　f.close

　　produces:

　　The line is: This is line one

　　The line is: This is line two

　　The line is: This is line three

　　以上就是Ruby中迭代器Iterator的使用教程，想必都了解了吧，更多相关内容请继续关注武林技术频道。