Scala 3/Reference/Other New Features/Parameter Untupling

Parameter Untupling

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Say you have a list of pairs

val xs: List[(Int, Int)]

and you want to map xs to a list of Ints so that each pair of numbers is mapped to their sum. Previously, the best way to do this was with a pattern-matching decomposition:

xs map {
   case (x, y) => x + y
}

While correct, this is also inconvenient and confusing, since the case suggests that the pattern match could fail. As a shorter and clearer alternative Scala 3 now allows

xs.map {
   (x, y) => x + y
}

or, equivalently:

xs.map(_ + _)

Generally, a function value with n > 1 parameters is converted to a pattern-matching closure using case if the expected type is a unary function type of the form ((T_1, ..., T_n)) => U.

Reference

For more information see: