Class Structure Hash

Purpose:
A request for comments on the notion of various equality tests for a class. The tests can be used in areas such as serialization, proxy/stub calls, versioning, dynamic type loading, etc.

Hash value are a SHA256 hash

Class-text hash:

• Complete hash of the text of the class. Any change including non-processed areas such as `note' or comments would cause the hash value to change.

Semantic-text hash:

• Hash value of the semantically-meaningful text of the class. This would ignore the actual character contents of breaks and would ignore comments and note fields. If a buggy version of a class is discovered, it could be rejected for serialization or connection by this hash value.

Attribute hash:

• Hash value of the attributes of the class. This would essentially mean anything with an equal attribute hash could be deserialized/serialized without recovery.

Feature hash:

• Name, signature, and export hash for a feature

Interface-to-class hash:

• Hash value of feature names and signature exported to a specific class. This would be useful for remote proxying. A class would have a additional value for each class to which features are exported. If class A exports features to {ANY}, {A}, {B}, and {NONE} it would have a hash value for each to say whether the interface exported to either ANY, A, or B has changed. Changes to features exported to A would affect the hash code for {ANY} and {A} but not {B}. Changes to features exported to NONE would not affect any hash values.

Contract hash:

• A hash value for a the contract of a feature.

Interface-to-class contract hash:

• A hash value for the contract of all features exported to a class.

Additional issues:

• Mutual recursive references. In some cases two classes reference each other; this could lead to difficulty in creating a hash value for both.
  
• Some traditionally non-semantic areas such as `note' actually have semantic value.
  
• Are 256 bits needed? Maybe truncate hash to 128 bits or 64 bits.