ruby的Comparable和Enumerable.md

Comparable

内置的 Comparable：

• :==
• :>
• :<
• :<=
• :>=
• :between?

将自定义的 class 变成 Comparable

class Person
  attr_reader :name
  include Comparable

  def initialize(name)
    @name = name
  end

  # 只需要定义 <=> 方法，就能将自定义 class 变成 Comparable
  # 这里定义了比较方法是根据 name
  def <=>(other)
    self.name <=> other.name
  end
end

p1 = Person.new "Andrea"
p2 = Person.new "Fabio"
p3 = Person.new "Luigi"

p p1 > p2 # false
p p2.between?(p1, p3) # true

Enumerable

1. search and filter
   • :all?
   • :any?
   • :detect (alias :find)
   • :drop
   • :find_all
   • :find_index
   • :include?
   • :none?
   • :one?
   • :reject
   • :select
2. grouping
   • :chunk
   • :group_by
   • :partition
3. iterate
   • :cycle
   • :each_slice
   • :each
   • :each_with_index
   • :reverse_each
4. iterate and create new collection
   • :each_with_object
   • :flat_map
   • :map
   • :inject
   • :sort
   • :zip
5. stats
   • :count
   • :max
   • :min
   • :minmax
   • :max_by
   • :min_by
   • :minmax_by
6. efficiency
   • :lazy

自定义的 class 变成 Enumerable

class Person
  attr_reader :people
  include Enumerable

  def initialize(people)
    @people = people
  end

  # 定义 each 方法，因为我们知道 people 是数组，所以可以直接调用 each 方法
  # 定义了 each 方法之后，其他的 enumerable 方法也有了
  def each
    raise "please provide a block" unless block_given?
    people.each do |person|
      yield person
    end
  end
end

p1 = Person.new ["Andrea", "Fabio", "Luigi"]
p1.each do |e|
  p e
end