hook__form_alter resetting &$form

I am doing some access to content using hook_form_alter as there are problems using hook_access with content types defined outside of your module. If a user does not have access I am setting a message at the top of the page and I don't want to output the form. I have the following code.

function mymodule_form_alter(&$form, $form_state, $form_id) {
    switch ($form_id) {
        case 'cmyformm':  
            dsm($form);
           $from = null;
            dsm($form);
            d开发者_JAVA技巧rupal_set_message('You do not have access to this page');
            break;
     }
}

The dsm however is returning the same information for $form even if I set it to null. How do I not display the form but a message?

I don't quite understand the question, but for starters you are setting $fROm to null and not $fORm. Setting for to null or just doing unset($form); should do the trick.

Access control shouldn't be done at the form level. Access control should be implemented with hook_access or in the router's access arguments. If you must do this at the form level, use user_access() along with the defined roles that you have.

In addition to the typo as pointed out by @zeroFIG, you are really doing this access check in the wrong way. I have used the node_example module with sucess on all node types - none were defined in the same module as the hook_access. Have a look here: http://api.drupal.org/api/examples/node_example--node_example.module/6