String removal from malloc

string_auto_clear.rb

class String
  def auto_clear
    begin
      result = yield self
      result.equal?(self) ? nil : result # avoid leaking
    ensure
      clear
    end
  end
end

#Then people can do this with Strings whose lifetime they know.

expr_returning_string.auto_clear do |str|
  puts "We got #{str}."
end