Ruby one line if return statement

Question

is there a way to shorten this line on Ruby?

if (res = bla_permission_invalid).is_a? String then return res end

on

def something # many things that like this
  if (res = bla_permission_invalid).is_a? String then return res end
  # do something else
  return true
end

when the content of bla_permission_invalid are something like

def bla_permission_invalid
  return invalid_address_report_func if invalid_address?
  return permission_error_report_func if @user.not_one_of? [ :group1, :group2 ]
  return nil
end

invalid_adress_report_func and permission_error_report_func returns string

Answer 1

If possible values are String and NilClass, then the code can be simplified to this:

def something
  res = bla_permission_invalid()
  return res if res # strings are truthy, so they'll be returned but nil will proceed

  # do something else
  true
end

Answer 2

def something
  bla_permission_invalid || (
  # do something else
  true)
end