Ruby之map、each、collect、map!、collect!揭秘

def map_method
  arr1 = ["name2","class2"]
  arr2 = arr1.map {|num| num + "and"}
  print "map............",arr2,"\n"
end

def each_method
  arr1 = ["name2","class2"]
  arr2 = arr1.each {|num| num + "and"}
  print "each............",arr2,"\n"
end

def collect_method
  arr1 = ["name2","class2"]
  arr2 = arr1.collect {|num| num + "and"}
  print "collect............",arr2,"\n"
end

def map1_method
  arr1 = ["name2","class2"]
  arr2 = arr1.map! {|num| num + "and"}
  print "map!............",arr2,"\n"
end

def collect1_method
  arr1 = ["name2","class2"]
  arr2 = arr1.collect! {|num| num + "and"}
  print "collect!............",arr2,"\n"
end

def test
  map_method
  each_method
  collect_method
  map1_method
  collect1_method
end

test

result：
map............["name2and", "class2and"]
each............["name2", "class2"]
collect............["name2and", "class2and"]
map!............["name2and", "class2and"]
collect!............["name2and", "class2and"]

为了更明了的了解each的用法，看下面的例子：

def each_deep_method
  arr_test = [1,2,3]
  arr_result = arr_test.each do |num|
    num = num + 1
    p num
  end
  arr_result
end

result:
2
3
4
=> [1, 2, 3]
可见each_deep_method的返回值arr_result是和arr_test相等的。
[总结]
(1)each只是遍历数组的每个元素，并不生成新的数组；
(2)map和collect相同用法，遍历每个元素，用处理之后的元素组成新的数组，并将新数组返回；
(3)map！同collect！
其中map和map！、collect和collect!的区别就不用纠结了吧，实在纠结就看下面的例子：

def map_deep_method
  arr_test = [1,2,3]
  arr_test.map do |num|
    num += 1
  end
  arr_test  #[1, 2, 3]
end

def map1_deep_method
  arr_test = [1,2,3]
  arr_test.map! do |num|
    num += 2 
  end
  arr_test  #[3, 4, 5]
end