type_validator.rb

require "ruby-boolean"
class TypeValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    value_to_test = type_before_coercion(record, attribute, value)
    expected_type = type_class(options[:with])

    record.errors.add attribute, (options[:message] || "argument of #{record.class} is not of class: #{options[:with].to_s.camelize}. It is class: #{value.class} with value of #{value}") unless value_to_test.is_a?(expected_type)
  end

  private

  def type_class(type)
    @type_class ||= type.is_a?(Class) ? type : symbol_class(type)
  end

  def symbol_class(symbol)
    {
      array: Array,
      boolean: Boolean,
      float: Float,
      hash: Hash,
      integer: Integer,
      string: String,
      symbol: Symbol,
      time: Time,
      date: Date,
      big_decimal: BigDecimal,
    }[symbol] || fail(UnsupportedType,
      "Unsupported type #{symbol.to_s.camelize} given for validates_type.")
  end

  def type_before_coercion(record, attribute, value)
    record.try(:"#{attribute}_before_type_cast") || value
  end

  class UnsupportedType < StandardError; end
end