Preserve class invariants

To preserve class invariants:

• Know the invariants in a class you design.
• Only allow an invariant to be invalid internally as long as it does not become visible outside the implementation of the class.
• Do not leave invariants invalid for too long.

The inline write functions of TStream modify the current position in the stream without checking the logical end. Thus, the class must catch up whenever it next gets a chance (that is, when a virtual function gets called). TStream must then infer the new logical end from the new stream position and other data members. If the computation is not performed immediately, that information can change again, and the new logical end will not be correctly computed.

In summary, learn what your invariants are and strive to keep them correct. The Assert function from the Test framework is very helpful. It allows you to test invariants when testing is turned on, but skips the check otherwise. If even that is too expensive, you can conditionally compile your assertions for debugging.