scala

Scala: Idiomatic Efficiency Reference

When to Use

• Use this skill when the task matches this description: Language-specific super-code guidelines for scala.

Table of Contents

1. [Collections & Functional Transforms](#collections)
2. [Pattern Matching](#patterns)
3. [Case Classes & ADTs](#case-classes)
4. [Option & Error Handling](#option)
5. [Implicits & Given/Using](#implicits)
6. [Concurrency](#concurrency)
7. [Anti-patterns specific to Scala](#antipatterns)

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1. Collections & Functional Transforms {#collections}

// ❌ Imperative accumulation
val result = new ArrayBuffer[String]()
for (item <- items) {
  if (item.isActive) result += item.name.toUpperCase
}

// ✅
val result = items.filter(_.isActive).map(_.name.toUpperCase)

// ❌ Manual grouping
val grouped = mutable.Map[String, List[Item]]()
for (item <- items) {
  grouped(item.category) = grouped.getOrElse(item.category, Nil) :+ item
}

// ✅
val grouped = items.groupBy(_.category)

// ❌ Manual fold when sum/product works
var total = 0
for (o <- orders) total += o.amount

// ✅
val total = orders.map(_.amount).sum

// ❌ Using head on potentially empty collection
val first = items.head // throws on empty

// ✅
val first = items.headOption // returns Option[T]

// ❌ Chaining filter + head for find
val found = items.filter(_.id == targetId).head

// ✅