Object-Oriented vs Functional, Plainly

Two ways of organizing code, demystified: what object-oriented programming actually is, what functional programming actually is, and the plain truth about which to reach for and when.

1. What OOP Actually Is Object-oriented programming bundles data together with the behavior that acts on it; encapsulation, inheritance, and polymorphism each solve a specific problem - here's the plain-language version of each.
2. What Functional Programming Actually Is Functional programming makes functions the core unit, avoids changing data in place (immutability), favors pure functions with no side effects, and builds big behavior by composing small functions - which is what makes the code easier to test and reason about.
3. Plainly: Which, When? The plain truth is that most real languages and codebases are both - OOP and FP are tools, not religions. Here's a fair comparison of where each one genuinely shines, with the judgment calls flagged as judgment.