Better Code: Exploring Validity in C++ - David Sankel - CppCon 2023

Exploring the concept of validity in C++ programming, including the meaning of invalid pointers, meaninglessness of broken objects, and the importance of invariants and language rules.

Key takeaways

An invalid pointer is not necessarily bad; it just means we cannot dereference it.
Memory that’s not owned by an object and cannot be destroyed or reassigned is equivalent to a broken object, representing meaningless state.
Validity also means the object’s state preserves its invariant, i.e. internal invariants and external interactions don’t change its status.
In the context of operations on objects, “valid for destruction” and “valid for assignments” refer to whether the object’s final state remains consistent.
An object doesn’t need to have a value by default; its value might be determined post-construction or at runtime (e.g., for a hash mapping function).
Validity ultimately boils down to ensuring the object or operation preserves its invariants against expected states.
The concept “meaningfulness” (or significance) goes beyond mere substantivity (or existence) involving both invariants and external interpretations.
There’s a distinction drawn between discardable items, which can be reassigned or demolished without issue, and broken, where it cannot.
Essence represents an object’s abstract model, often involving both substance representation and invariant guarantees.
Terminology for discussing validly assigned pointers is crucial while programming in C++.
Another approach is using the concept of “liveness” or “unbrokeneness, meaning that objects that are operational should be able to continue usage.
Validity is not confined to only these two specific scenarios but extends to other more specific scenarios and object types according to specific language rules about value types.
Additionally, some code snippets discuss whether it is essential to document objects or invariants, demonstrating potential pitfalls with code comprehension, which leads to misinterpretation or error.
As with meaningfulness``discardable`` and valid for destructionvalid with respect to fit means it meets the post-condition specified in the function it belongs to.

Better Code: Exploring Validity in C++ - David Sankel - CppCon 2023

More talks