  Correctness-by-Construction (CbC) is an incremental program construction
process to construct functionally correct programs. The programs are
constructed stepwise along with a specification that is inherently guaranteed
to be satisfied. CbC is complex to use without specialized tool support, since
it needs a set of predefined refinement rules of fixed granularity which are
additional rules on top of the programming language. Each refinement rule
introduces a specific programming statement and developers cannot depart from
these rules to construct programs. CbC allows to develop software in a
structured and incremental way to ensure correctness, but the limited
flexibility is a disadvantage of CbC. In this work, we compare classic CbC with
CbC-Block and TraitCbC. Both approaches CbC-Block and TraitCbC, are related to
CbC, but they have new language constructs that enable a more flexible software
construction approach. We provide for both approaches a programming guideline,
which similar to CbC, leads to well-structured programs. CbC-Block extends CbC
by adding a refinement rule to insert any block of statements. Therefore, we
introduce CbC-Block as an extension of CbC. TraitCbC implements
correctness-by-construction on the basis of traits with specified methods. We
formally introduce TraitCbC and prove soundness of the construction strategy.
All three development approaches are qualitatively compared regarding their
programming constructs, tool support, and usability to assess which is best
suited for certain tasks and developers.
