oberonjs/doc/wiki/eberon-record-fields-read-only-export.md

Read-only export is introduced for record fields using '-' mark - in the same way as it is done in Component Pascal. The major reason for this extension is to maintain data integrity without obligation to write down corresponfing procedures-accessors. I.e. instead of hiding (not exporting) record field and giving procedure-accessor (exported) for reading field value it is possble to just mark a field as exported for reading only.

Syntax

identdef = ident ["*" | "-"].

Example:

MODULE m1;
TYPE 
    T* = RECORD
        i-: INTEGER
    END;
    TP* = POINTER TO T;

    PROCEDURE make*(): TP;
    VAR result: TP;
    BEGIN
        NEW(result);
        result.i := 123; (* field 'T.i' can be modified in this module *)
        RETURN result
    END make;
END m1.    

MODULE m2;
IMPORT m1;
VAR p: m1.TP; 
BEGIN
    p := m1.make();
    ASSERT(p.i = 123); (* field 'T.i' can be accessed in this module *) 
    p.i := 321; (* compiller error, 'T.i' cannot be modified in this module *)
END m2.