举例讲解Ruby中迭代器Iterator的用法
Iterator A Ruby iterator is simple a method that can invoke a block of code.
def two_times yield yield end two_times { puts "Hello" } # Hello # Hello def fib_up_to(max) i1,i2 = 1. 1 while i1 <= max 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。 常见的 iterator 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 [1,4,9].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. [1,7].inject { |sum,element| sum + element } # => 16 # sum = 1,element = 3 # sum = 4,element = 5 # sum = 9,element = 7 # sum = 16 [1,6].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: [1,7].inject(:+) # => 16 [1,7]/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:
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