Railsのpresent? blank? presence あたりの定義

自分用メモ。

Rails 5.2.3のソースだと

activesupport/lib/active_support/core_ext/object/blank.rb

class Object
  # An object is blank if it's false, empty, or a whitespace string.
  # For example, +false+, '', '   ', +nil+, [], and {} are all blank.
  #
  # This simplifies
  #
  #   !address || address.empty?
  #
  # to
  #
  #   address.blank?
  #
  # @return [true, false]
  def blank?
    respond_to?(:empty?) ? !!empty? : !self
  end

  # An object is present if it's not blank.
  #
  # @return [true, false]
  def present?
    !blank?
  end