scala-option-either

Scala Option, Either, and Try for Python Developers

Core Concept: Functional Error Handling

Python uses None and Optional[T] to represent absence. Scala uses types that can be pattern-matched:

Python	Scala	Purpose
None	None (in Option)	Represents absence
Optional[T] / T | None	Option[T]	Represents presence or absence
Exception handling	Either[Err, Success]	Represents error or success
Exception handling	Try[T]	Like Either but for exceptions

Option[T] - Replace None/Optional

Python Pattern

def safe_divide(a: float, b: float) -> float | None:
    if b == 0:
        return None
    return a / b

result = safe_divide(10, 2)
if result is not None:
    print(f"Result: {result}")
else:
    print("Division by zero")

Scala Pattern

def safeDivide(a: Double, b: Double): Option[Double] =
  if (b == 0) None else Some(a / b)

// Pattern matching
safeDivide(10, 2) match {
  case Some(result) => println(s"Result: $result")
  case None => println("Division by zero")
}

// Or functional style
safeDivide(10, 2).foreach(result => println(s"Result: $result"))

Key Option Methods

val opt: Option[Int] = Some(42)

// Extraction
opt.get        // 42 (throws if None - avoid!)
opt.getOrElse(0)  // 42
opt.orElse(Some(0))  // Some(42)

// Transformation
opt.map(_ * 2)    // Some(84)
opt.flatMap(x => Some(x * 2))  // Some(84)
opt.filter(_ > 40)  // Some(42)

// Iteration
for (v <- opt) println(v)  // prints 42

// Checking
opt.isDefined   // true
opt.isEmpty     // false

Either[L, R] - Represent Success or Failure

Either is more powerful than Option - it carries error information.

Python Pattern

def validate_age(age: int) -> tuple[bool, str | None]:
    if age < 0:
        return False, "Age cannot be negative"
    if age > 150:
        return False, "Age seems unrealistic"
    return True, None

success, error = validate_age(-5)
if not success:
    print(f"Error: {error}")