[Issue 2412] New: Hole in type system: array conversion to supertypes

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=2412

           Summary: Hole in type system: array conversion to supertypes
           Product: D
           Version: 1.035
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Keywords: accepts-invalid, spec
          Severity: major
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla at digitalmars.com
        ReportedBy: fraserofthenight at gmail.com


Automatic conversion of an array of a subtype to an array of its supertype
creates a hole in the type system (that is, you can get an invalid type without
doing any casting). Consider the following legal D code:

module bug;

class A { }
class X : A { void hello() { } }
class Y : A { }

void main()
{
    X[] xArray = new X[1];
    A[] aArray = xArray;
    aArray[0] = new Y();
    X x = xArray[0];       // Automatic conversion of Y -> X without cast
    x.hello();             // Likely segfault
}

The solution is to require an explicit cast from X[] to A[] (that is, any
subtype array to its supertype).


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