currentUserField() and core User fields

Question

Hello, 
 I was wondering if one of you can answer this question : why core user fields are not available for the currentUserField () formula ? 
 Is there a logical reason I am missing that explains this ? 
 Because, while digging in the code, we understand that one property was missing for core fields ( calculation_visible ) but it seems that other vardefs properties are involved. 
 For instance, we were looking on an easy way to set a field as readonly if you are not an admin. The admin field is a core user field. We are able to customize the sugarfield_is_admin.php file and include 
 
 $dictionary['User']['fields']['is_admin']['calculation_visible']=true; 
 
 But another property is missing for this field : $def['studio']['related' ] . 
 Because is_admin is a important field, we don't want to play with the studio.related property that we currently don't understand. Is someone aware about this vardefs property ? 
 
 Many thanks for your help. 
 
 Fred

the code I am talking about : 
 
 include/Expressions/Expression/Generic/CurrentUserFieldExpression.php 
 modules/ExpressionEngine/formulaHelper.php with cleanFields function used from getValidUserFields function

Frédéric Rinaldi · Answer

Hi Frédéric Rinaldi , 
 
 I haven't personally modified the vardefs of is_admin and cannot say for certain why it is not made available. To accomplish this use case in the past, here is what I did: 
 
 Create a checkbox field in the Users module (e.g. administrator_check_c) with the following attributes: 
 
 Calculated: $is_admin 
 Make visible for calculations: checked

In the read-only formula, I reference that new field: not(
 currentUserField(
 $administrator_check_c
 )
) 
 
 Chris