Spending some amount of time on parameter packs, I wanted to provide some feedback on the current state of parameter packs in Variadic Generics.
Firstly, I often find myself writing code that looks a bit hacky and may be difficult to read due to the lack of something like "repeat" block. For instance, I end up using nested function like the following:
func someVariadicGenericFunction<each T>(argument: repeat each T) -> Value {
var result: Value = Value()
func update<U>(with argument: U) {
result = someFunction(argument)
}
repeat update(with each argument)
return result
}
It would be simpler and cleaner if we had something like repeat block:
var result: Value = Value()
repeat {
result = someFunction(each argument)
}
return result
Secondly, it is currently not possible to reuse value packs in a variadic function like print(repeat each value) . Although the syntax itself was accepted as part of SE-0393, it requires another proposal before it can be implemented, as mentioned in this comment. I believe this is a small but important improvement, and I hope to see a proposal for it soon.
Lastly, while trying to implement a variadic ChainSequence in Swift Algorithms, I encountered difficulties in conforming to Collection due to the lack of something like a "variadic union type." Specifically, I couldn't implement a variadic version of this section.
Although I don't have a concrete suggestion to enable this kind of variadic generics, I believe it is an issue worth addressing.