Ruby class extensions for accessing object values by keypath

keypath.rb

module Keypathable

  ## Operators
  ####
  
  # Non mutating operator
  def >(keypath)
    if self.is_a?(Array) || self.is_a?(ActiveRecord::Associations::CollectionProxy)
      return self.values_for_keypath(keypath)
    else
      return self.value_for_keypath(keypath)
    end
  end

  # Mutating operator
  def <(keypath)
    if self.is_a?(Array) || self.is_a?(ActiveRecord::Associations::CollectionProxy)
      return self.values_for_keypath!(keypath)
    else
      warn "WARNING: Cannot mutate #{self.class.name}"
      return self
    end
  end

  ## Implementation
  ####

  # Returns a copy of the Array mapped to the object returned by calling value_for_keypath on each member
  def values_for_keypath(keypath)
    unless self.respond_to?(:map)
      warn "WARNING: #{self.class.name} doesn't respond to `map`"
      return self
    end
    return self.map{|item| item.value_for_keypath(keypath) }
  end

  # Returns a mutates self mapped o the object returned by calling value_for_keypath on each member
  def values_for_keypath!(keypath)
    unless self.respond_to?(:map!)
      warn "WARNING: #{self.class.name} doesn't respond to `map!`"
      return self
    end
    return self.map!{|item| item.value_for_keypath(keypath) }
  end

  # Returns a value (if it exists) at the keypath relative to self
  def value_for_keypath(keypath)
    return self if keypath.blank?

    keys = keypath.split(".")
    value = self

    if !value.respond_to?(keys.first)
      return nil
    end

    if keys.count > 1
      # This is not truly recursive, but it works fine
      keys.each do |k|
        value = value.value_for_key(k)
        break if value.nil?
      end
    else
      return value_for_key(keys.first)
    end

    return value
  end

protected

  def value_for_key(key)
    if self.is_a?(String)
      return nil
    elsif self.is_a?(Hash)
      return self.dig(key)
    elsif self.is_a?(Object)
      return self.send(key) if (self.respond_to? key)
      return nil
    end
  end

end

class Object
  include Keypathable
end

class Array
  include Keypathable
end

class ActiveRecord::Associations::CollectionProxy
  include Keypathable
end