How dependencies make C++ systems hard to test and evolve—and why functional thinking changes it Fighting complexity is crucial if you want to succeed in software development. In many real-world C++ projects, however, systems tend to evolve in the opposite direction. Components become tightly coupled, so changes ripple through large parts of the system. State is scattered, reducing transparency about how it evolves over time. Behavior emerges from many interacting parts, making it hard to reason about individual pieces in isolation. This also shows up in testing: a significant amount of boilerplate and indirection is needed just to enable it. Establishing specific system states requires substantial setup, and maintaining tests becomes costly, as even small production changes force updates across large parts of the test code. The result is a system that is hard to get right—and once it works, it feels rigid and difficult to evolve.…