C++ Kraków - Preconditions, Postconditions, Invariants: How They Help Write Robust Programs

After a long break, we are reasuming with the online meetings.

This is going to be a high-level overview of certain notions related to program correctness: (a) function contract, (b) precondition, (c) postcondition, (d) invariant.

Even if you are not familiar with these terms you are probably using them already, as they are key to writing correct programs.

In this talk we will see:

1. How thinking in these terms helps us write code more consciously and with fewer bugs.

2. How these terms are reflected today in code (spoiler: comments, assert() and "contract-encoding" types).

3. How different tools, like static analyzers or IDEs, can be improved if things like preconditions can be expressed directly in code.

4. What the difference is between a bug and a symptom of a bug, and how to fix bugs rather than conceal their symptoms.

No prior knowledge of the subject is assumed. By the end of the talk:

1. You will appreciate and be willing to apply the Design by Contract methodology, even if it means putting more asserts() and comments in your code.

2. You should be able to tell why a "contract" is not a sum of preconditions, postconditions and invariants.

3. You will understand how "contract-encoding" types and preconditions/invariants are complementary features.

We had a similar presentation in 2019 (https://www.meetup.com/C-User-Group-Cracow/events/262313721/). This is going to be an updated version.