The elimination form for Algebraic Data Types. Inspects which variant a sum type holds and destructures the fields of a product type in a single expression.
Exhaustiveness checking ensures every variant is handled at compile time, making illegal states unrepresentable and unhandled cases impossible.
In Rust: match. In Haskell: case expressions and function clause definitions. In C++17: std::visit over std::variant.
Distinct from regex pattern matching or string matching. This is structural pattern matching over the shape of data.