Variadic parameters

Decided

D-0056, settled by the language’s author: part of spec §18. Older text cites it as 18.56.

name: ..T, last, seen as a read-only []T; f(..xs) spreads a slice as the only variadic argument; C varargs stay unimported. The caller builds a temporary array, so there is no allocation and nothing is instantiated per call. Arguments of different types go through a trait reference (..&Format), which is what a library println needs. Chosen over same-type-only, which leaves println a builtin forever, and over compile-time packs (C++ Ts...), which cannot be walked without macros (M10). .. rather than ...: it already means “a run of” and needs no new token. A spread is explicit, so a []T argument is never silently one element or many (§7.2). “Last” is revised by 18.72: there is at most one, and the parameters after it are passed by name