Type hints, called type annotations, attach explicit type information to parameters, results, or function values. In Scala, a parameter such as `n: Int` declares its type, while `: Int` after a method signature declares the result type. Scala can often infer omitted types, but explicit result annotations clarify public methods. section 2.1
Type annotations support several closely related readings:
- They document a method’s signature: `def abs(n: Int): Int` takes an integer and returns an integer. section 2.1
- They describe function values: `(Int, Int) => Boolean` means a function taking two integers and returning a Boolean. section 2.4.2
- They can be omitted when Scala infers function-argument types from context, as with `(x, y) => x < y`. section 2.4.2
Listing 2.1 A simple Scala program
// A comment!
/* Another comment */
/** A documentation comment */
object MyProgram: #1
def abs(n: Int): Int = #2
if n < 0 then -n #3
else n
private def formatAbs(x: Int) = #4
val msg = "The absolute value of %d is %d" #5
msg.format(x, abs(x)) #6
@main def printAbs: Unit = #7
println(formatAbs(-42))
The listing places parameter annotations, an explicit public result annotation, and an inferred private result side by side. section 2.1
