ruby - 为什么我使用注入重构的红宝石不起作用？

Question

我尝试进行一些重构以将每个块转换为注入，但它不起作用，我不明白为什么。

这是重构之前的代码：

class String
  # Build the word profile for the given word. The word profile is an array of
  # 26 integers -- each integer is a count of the number of times each letter
  # appears in the word. 
  #
  def profile
    profile = Array.new(26) { 0 }
    self.downcase.split(//).each do |letter|
      # only process letters a-z
      profile[letter.ord - 'a'.ord] += 1 unless letter.ord > 'z'.ord
    end
    profile
  end
end

这是我的重构不起作用：

class String
  # Build the word profile for the given word. The word profile is an array of
  # 26 integers -- each integer is a count of the number of times each letter
  # appears in the word. 
  #
  def profile
    self.downcase.split(//).inject(Array.new(26) {0}) do |profile, letter|
      # only process letters a-z
      profile[letter.ord - 'a'.ord] += 1 unless letter.ord > 'z'.ord 
    end
  end
end

当我尝试执行重构的方法时，我得到

`block in profile': undefined method `[]=' for 1:Fixnum (NoMethodError)

如果我理解正确，它不喜欢我重构版本中配置文件对象上的数组引用运算符，这意味着传递给注入的初始化程序不起作用。这种理解正确吗？如果是这样，为什么不呢？

谢谢！

Answer 1

The []= method returns the assigned value, so the value of profile in the next iteration will be 1 (since it's the value of the last iteration). In order to get the behavior you want, you'll have to do:

self.downcase.split(//).inject(Array.new(26) {0}) do |profile, letter|
  # only process letters a-z
  profile[letter.ord - 'a'.ord] += 1 unless letter.ord > 'z'.ord 
  profile
end

or

self.downcase.split(//).inject(Array.new(26) {0}) do |profile, letter|
  # only process letters a-z
  profile.tap { profile[letter.ord - 'a'.ord] += 1 unless letter.ord > 'z'.ord }
end