Only static data that is allowed to exist is data that could not provide communication channel. For exmple static mutable variables will prohibited.
So only immutable static data should be allowed.
Implementing it fully will require proof carying code methodology in or to create proofs that data is immuable.
As temporary soluition for prototype, only some specific types will be allowed to qualify as immutable types. Here is complete definitio of them:
List of types allowed for cosntants in prototype
Primitive integer types
String type, and possilby limited list of other types like BigInteger, BigDecimal etc.
Compound type composed only from other immutable types w/o methods that are preforming write outside of constructors. Enumeration type will qualify here. Note that verifier will reject all attempts to modify fields of non mutabe values. Value should be hosted in mutable cell in order to be allowed modified.
Boxed immutable type.
Const array of immutable type.
If you think that something here could provide a communcation channel and should be forbidden please notify me. Also if you think some easy to verify rule that will extend list of valid types could be added here, also please notify me.