Pure-Ruby port of MRI's Hash class

hash.rb

class MyHash
  include Enumerable

  def initialize(data=nil, capacity=11)
    @capacity = capacity
    @data = Array.new(capacity) { [] }
    @keys = []

    return unless data
    data.each do |key, value|
      self[key] = value
    end
  end

  def []= key, value
    hash = key.hash % @capacity
    @data[hash].each_with_index do |pair, index|
      if pair[0].eql? key
        return pair[1] = value
      end
    end

    @keys << key
    @data[hash] << [key, value]
    rehash if @keys.length > @capacity * 5
    value
  end

  def [] key
    hash = key.hash % @capacity
    @data.fetch(hash).each_with_index do |(k, v), index|
      if k.eql? key
        return @data[hash][index][1]
      end
    end
  end

  def inspect
    str = '{'

    str << @keys
      .map { |key| "#{key.inspect}=>#{self[key].inspect}" }
      .join(', ')

    str << '}'
  end

  def keys
    @keys
  end

  def each
    @keys.each do |key|
      yield key, self[key]
    end
  end

  def delete key
    hash = key.hash % @capacity
    index = @data[hash].index { |pair| pair[0].eql? key }
    return unless index

    @keys.delete key
    pair = @data[hash].delete_at index
    pair[1]
  end

  def rehash
    data = @keys.map { |key| [key, self[key]] }
    @capacity = @keys.length
    @data = Array.new(@capacity) { [] }
    data.each do |pair| 
      hash = pair[0].hash % @capacity
      @data[hash] << pair
    end
  end
end