Vararg Splices
The syntax of vararg splices in patterns and function arguments has changed. The new syntax uses a postfix *, analogously to how a vararg parameter is declared.
val arr = Array(0, 1, 2, 3)
val lst = List(arr*) // vararg splice argument
lst match
case List(0, 1, xs*) => println(xs) // binds xs to Seq(2, 3)
case List(1, _*) => // wildcard pattern
The old syntax for splice arguments will be phased out.
/*!*/ val lst = List(arr: _*) // syntax error
lst match
case List(0, 1, xs @ _*) // ok, equivalent to `xs*`
Syntax
ArgumentPatterns ::= ‘(’ [Patterns] ‘)’
| ‘(’ [Patterns ‘,’] Pattern2 ‘*’ ‘)’
ParArgumentExprs ::= ‘(’ [‘using’] ExprsInParens ‘)’
| ‘(’ [ExprsInParens ‘,’] PostfixExpr ‘*’ ‘)’
Compatibility considerations
To enable cross compilation between Scala 2 and Scala 3, the compiler will accept both the old and the new syntax. Under the -source future setting, an error will be emitted when the old syntax is encountered. An automatic rewrite from old to new syntax is offered under -source future-migration.
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