How-To Guides on Advanced Beginner

Implicit/Given Debugging

d8lzz1gpw@mozmail.com (kimbenji) — Fri, 16 Jan 2026 00:00:00 +0000

Learn how to diagnose and resolve issues when the compiler cannot find implicit values.

Estimated time: 10-15 minutes

TL;DR

Scala 2: Use -Xlog-implicits flag to trace the search process

Scala 3: Compiler messages are clearer and provide import suggestions

Common: Check if implicit values are in scope and types match exactly

What This Guide Solves#

Use this guide when you encounter these compile errors:

Scala 2

could not find implicit value for parameter ord: Ordering[MyClass]

Future Error Handling

d8lzz1gpw@mozmail.com (kimbenji) — Fri, 16 Jan 2026 00:00:00 +0000

Learn how to safely handle and debug exceptions in asynchronous code.

Estimated time: 15-20 minutes

TL;DR

recover/recoverWith: Handle specific exceptions and return fallback values

transform: Transform both success and failure cases

onComplete: Use only for side effects (logging, etc.)

Never do this: Use Await.result to throw exceptions synchronously

What This Guide Solves#

Use this guide when:

Exceptions in Future silently disappear
You don’t know how to handle errors in asynchronous code
You need to decide between recover, recoverWith, and transform

Symptoms#

import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global

val future = Future {
 throw new RuntimeException("Something went wrong")
}
// Program exits normally, but where did the exception go?

What This Guide Does NOT Cover#

Basic Future concepts: See Concurrency Concepts
Cats Effect IO / ZIO error handling: Refer to respective library documentation
Akka actor system error handling: Refer to Akka documentation

Before You Begin#

Ensure you have the following environment ready:

Type Error Debugging

d8lzz1gpw@mozmail.com (kimbenji) — Mon, 23 Mar 2026 00:00:00 +0000

This guide walks you through decoding and resolving complex type error messages.

Estimated time: About 15-20 minutes

TL;DR

Type Mismatch: Compare expected and actual types to find where the mismatch occurs

Bounds violation: Check upper/lower bound constraints on type parameters

Variance issues: Verify that the correct types appear in covariant/contravariant positions

splain plugin: Transforms complex type errors into a more readable format

Problems This Guide Solves#

Use this guide when you encounter the following compilation errors:

Resolving sbt Dependency Conflicts

d8lzz1gpw@mozmail.com (kimbenji) — Mon, 23 Mar 2026 00:00:00 +0000

This guide walks you through diagnosing and resolving library version conflicts.

Estimated time: About 15-20 minutes

TL;DR

Symptom: Compilation succeeds but NoSuchMethodError or ClassNotFoundException occurs at runtime

Diagnosis: Use sbt dependencyTree to identify conflicting libraries

Resolution: Use exclude, dependencyOverrides, or force()

Prevention: Do not ignore eviction warnings

Problems This Guide Solves#

Use this guide in the following situations:

Compilation succeeds but NoSuchMethodError occurs at runtime
ClassNotFoundException occurs even though the library is clearly present
Eviction warnings appear during the sbt build
Multiple libraries require different versions of the same dependency

Symptoms#

# Compilation succeeds but error at runtime
$ sbt run
java.lang.NoSuchMethodError: 'void com.google.common.collect.ImmutableMap.forEach()'

# Or class not found
$ sbt run
java.lang.ClassNotFoundException: org.apache.commons.lang3.StringUtils

What This Guide Does Not Cover#

sbt basics: See the official sbt documentation
Maven/Gradle dependency management: See the respective build tool documentation
Scala binary compatibility: Compatibility between Scala versions is a separate topic

Before You Begin#

Verify the following environment is ready:

Performance Profiling

d8lzz1gpw@mozmail.com (kimbenji) — Mon, 23 Mar 2026 00:00:00 +0000

This guide walks you through finding and optimizing performance bottlenecks in Scala applications.

Estimated time: About 20-25 minutes

TL;DR

CPU profiling: Identify hotspots with JFR (Java Flight Recorder)

Memory analysis: Analyze heap dumps with VisualVM or MAT

Collection selection: Choosing the right collection for the job can make a significant performance difference

Optimization techniques: @specialized, @tailrec, avoiding boxing

Problems This Guide Solves#

Use this guide in the following situations:

Your application’s response time has suddenly become slow
Memory usage is continuously increasing (suspected memory leak)
You need to decide which collection to use from a performance perspective
GC pauses are occurring frequently

What This Guide Does Not Cover#

JVM tuning (GC options, etc.): See the official JVM documentation
Distributed system performance optimization: This is a separate topic
Cats Effect / ZIO performance optimization: See the respective library documentation

Before You Begin#

Verify the following environment is ready: