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Scala and the JVM · Part 20
A hand-written unapply turns a catch block into a policy: pass your own errors through, wrap recoverable JVM exceptions, and let fatal ones propagate. A runnable Scala 2.13 demo shows exactly when the matcher calls it.
Scala and the JVM · Part 19
A sealed trait removes impossible states from a model, but five details decide whether it holds: constructors, exhaustivity warnings, wildcards, Scala 2 inference and secrets in toString. I compiled each one on Scala 2.13.18.
Scala and the JVM · Part 3
From Java Optional to Scala Option: represent presence with Some, absence with None, and handle both outcomes with a match expression using our runnable policy lookup.