I have done this in the past.. Pretty sure of it.. But facing issues in 19.1, even following the help example.

Using a function as an expression for a DEO entry_item.

I tried all sort of things.. moving the function to DDO like the sample in the help. Placing it into the same DEO object.
Also tried to use RefFunc function.. but all with same result.

Code:
    
    Object oInputJson is a cdbTextEdit

        Function CalcExtended Returns String
            Number nExtent

            Move (29.3 * 43.4) to nExtent
    
            Function_Return (String(nExtent))
        End_Function
        
        Entry_Item (CalcExtended(Self))
        Set Size to 121 291
        Set Location to 48 88
        Set Label to "JSON"
    End_Object
Returns in error 68 when opening the view by the 1st time:
Code:
E:\Projetos\DataFlex\DAW Examples\Exemplos_JSON_Db2\Programs\ExemplosJSON.exe
Impossível criar item

Erro: 68

GET_ACTIVATE_OPERSONBSON_HANDLE (10298) - oClientArea (242) - at address 70740
MSG_ACTIVATE_OPERSONBSON (10299) - oClientArea (242) - at address 70696
MSG_ONEXECUTE (8103) - oPersonBSONMenuItem (144) - at address 68466
MSG_EXECUTE (8102) - oPersonBSONMenuItem (144) - at address 46729
MSG_ONCOMEXECUTE (7149) - oCommandBarSystem (101) - at address 45719
[start] - at address 70765
The offending line is the Entry_Item command

Regards