These days, the declarative programming style is used in a variety of cases, even if not in its purest form. However, the method is not suitable for all uses.
Declarative code is characterized by a high level of abstraction. This enables developers to represent complex programs in a compressed form. But the more sophisticated the application, the greater the danger that the code becomes so convoluted that it can only be read by the developer who originally wrote it. For companies that want to be able to maintain and develop applications without having to rely on a single person’s knowledge, this presents a challenge. External developers have to carefully read and work out the declarative code until they understand the structure and have solved any problems.
However, the level of abstraction in declarative programming also offers advantages. Because implementation is clearly delineated from the system using an algorithm, maintenance can be performed independently of application development. Interruptions of day-to-day operations are reduced to a minimum. At the same time, optimization is easier because the algorithm used allows new methods to be integrated. One disadvantage of algorithm use is that this kind of formulaic solution is often insufficiently equipped to deal with specific characteristics of individual applications.
Not so much a disadvantage as a challenge is the conceptual model of declarative programming. Thinking in terms of solution states contradicts natural human thought processes. People tend to think in terms of processes moving towards a goal rather than starting from a goal and working backward. This requires developers to rethink and accustom themselves to the concept, which can initially slow down problem-solving. However, once the new mindset has been learned, the declarative approach can capitalize on its strengths.
Another advantage of development starting from the description of the problem is that teams can outline solution models rapidly. Ultimately, specific programming of the implementation can take place later. The declarative style is thus well suited for prototyping in agile software development.