The Visitor pattern, which is a must in certain niches is exactly analogous to pattern matching over a sum type, and I am fairly certain that I can objectively

The Visitor pattern, which is a must in certain niches is exactly analogous to pattern matching over a sum type, and I am fairly certain that I can objectively say that the latter is a million times more readable and maintainable. It doesn’t make OOP obsolete, though, at all. Certain other areas are better expressed as hierarchies, e.g. GUI nodes.