Question

想象一下以下代码：

class SimpleLetter
  def values
    ("a" .. "z").to_a
  end

  def ===(other)
    values.include?(other)
  end
end

class Vowel < SimpleLetter
  def values
    ["a","e","i","o","u"]
  end
end

class Consonant < SimpleLetter
  def values
    super - Vowel.new.values
  end
end

objects = ("a" .. "f").to_a + (1 .. 5).to_a

objects.each do |letter|
  case letter
    when Vowel.new
      puts "#{letter} it's a vowel"
    when Consonant.new
      puts "#{letter} it's a consonant"
    else
      puts "#{letter} it's something else"
  end
end

我可以选择任何其他类，我只是以它们为例。我非常喜欢Scala的match和提取器，我认为这可能是在Ruby中编写相同内容的好方法。是否有更好的方法来编写上述内容而不必实例化新对象，这样我就可以调用他们的===方法？

为了避免不必要的帖子，是的，我知道我可以这样做：

case letter
  when ["a","e","i","o","u"].include?(letter)
    # ...
end

Answer 1

您不需要角色类。将它们设置为数组，并在case语句中使用splat运算符。

SimpleLetter = ("a" .. "z").to_a
Vowel        = %w[a e i o u]
Consonant    = SimpleLetter - Vowel

(("a" .. "f").to_a + (1 .. 5).to_a).each do |letter|
  case letter
    when *Vowel
      puts "#{letter} it's a vowel"
    when *Consonant
      puts "#{letter} it's a consonant"
    else
      puts "#{letter} it's something else"
  end
end

Answer 2

===也适用于块：

Letters = ('a'..'z').to_a
Vowels = ['a','e','i','o','u']
Consonants = Letters - Vowels

Vowel = lambda { |x| Vowels.include? x }
Consonant = lambda { |x| Consonants.include? x }

objects = ("a" .. "f").to_a + (1 .. 5).to_a

objects.each do |object|
  case object
    when Vowel
      puts "#{object} is a vowel."
    when Consonant
      puts "#{object} is a consonant."
    else
      puts "#{object} is an object."
  end
end

Answer 3

您可以使用类方法而不是实例方法：

class SimpleLetter
    def self.values
        ("a" .. "z").to_a
    end 

    def self.===(other)
        values.include?(other)
    end 
end

class Vowel < SimpleLetter
    def self.values
        ["a","e","i","o","u"]
    end 
end

class Consonant < SimpleLetter
    def self.values
        super - Vowel.values
    end 
end

objects = ("a" .. "f").to_a + (1 .. 5).to_a

objects.each do |letter|

    case letter
        when Vowel
            puts "#{letter} it's a vowel"
        when Consonant
            puts "#{letter} it's a consonant"
        else
            puts "#{letter} it's something else"
    end 

end

Answer 4

你困惑我的代码，因为SimpleLetter应该是一个字母，而不是整个字母。

尽管monkeypatching有点风险，但我还是有一半想做以下事情：

module Voweliness
  def vowel?
    self =~ /[aeiou]/i
  end

  def consonant?
    (self =~ /[a-z]/i and not vowel?)
  end
end

class String
  include Voweliness
end


objects.each do |letter|
  case
    when letter.vowel?
      puts "#{letter} is a vowel"
    when letter.consonant?
      puts "#{letter} is a consonant"
    else
      puts "#{letter} is something else"
  end
end

Answer 5

你已经有几个很好的答案（例如sawa's），所以我在一个没有case声明的情况下包括一个有趣的答案：

SIMPLE_LETTER = [*"a" .. "z"]
VOWEL        = %w[a e i o u]
CONSONANT    = SIMPLE_LETTER - VOWEL

[*?a..?f,*1..5].each do |letter|
  letter_class = %w(vowel consonant).select { |c| Object.const_get(c.upcase).include? letter}.first
  puts "'#{letter}': #{ letter_class || "something else"}"
end

输出：

'a': vowel
'b': consonant
'c': consonant
'd': consonant
'e': vowel
'f': consonant
'1': something else
'2': something else
'3': something else
'4': something else
'5': something else

多splat和字符文字仅适用于1.9。

有没有比使用自定义case语句更实用的方法在Ruby中编写它？

5 个答案: