type_check.rb

# Check types
def type_check(checks)
  checks.each do |var, types|
    types = types.is_a? Array ? types : [types]
    match = false
    types.each { |type| match = true if var.is_a? type }
    raise ArgumentError unless match
  end
end

# Usage
def self.localized_tree(locale, dialect, page_opts = {})
  type_check(
    locale    => [Locale, Numeric], 
    dialect   => [Dialect, Numeric], 
    page_opts => Hash
  )
  # Do some other stuff
end