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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 18
I replaced this site's Spring Boot backend with Scala 2.13, Play 3, Anorm and Twirl in one pull request. The rewrite was the easy part: this is how I fixed the contracts, kept the outbox wire format, and rehearsed the rollback on a restored production backup.
Scala and the JVM · Part 17
I connect Future composition and recovery to the map/flatMap pattern, reproduce one-worker starvation safely, and finish with the distinction between a business Left and a failed Future.
Scala and the JVM · Part 16
I replace String failures with a sealed family of domain errors, keep Either composition unchanged, and choose human-readable messages only at the display boundary.
Scala and the JVM · Part 15
I unpack AnyFunSuite from a Java developer’s perspective, test returned Right and Left values, check thrown exceptions with intercept, and verify that independent expectations catch real mistakes.
Scala and the JVM · Part 14
From Java-style exception handling to composable Scala results: capture a throwing conversion, understand map versus flatMap, write the same chain with for, and recover only from a specific failure.
Scala and the JVM · Part 13
From a Java/Spring perspective, I build Scala Either from explicit Left/Right cases to map, flatMap and a for-comprehension, with three verified lookup outcomes and failure reasons that survive the chain.
Scala and the JVM · Part 12
Coming from Java, a String with a lookup method looks wild. I unpack Scala 2 implicit classes into an ordinary wrapper, then show how the compiler can supply its repository argument too.
Scala and the JVM · Part 11
From multiple parameter lists to compiler-supplied repository arguments: real missing and ambiguous implicit errors, explicit fixes, and the difference between a missing dependency and a missing policy.