> Half-digression into relational theory aside, I can’t figure a way to make
> the compiler enforce this. An enum is "exactly one", a Set is "zero or more",
> a structure or class is "this group", an Optional is "zero or one".
You can write an enum that's "one or more":
enum OneOrMore<Element> {
case one (Element)
indirect case more (first: Element, rest: OneOrMore<Element>)
}
Or, equivalently:
struct OneOrMore<Element> {
var first: Element
var rest: [Element]
}
`first` could instead be `last`, of course; I've done it this way because
`reduce` is a left fold.
It should be possible to conform either of these to Collection or even
MutableCollection, but not to RangeReplaceableCollection, which assumes you can
create an empty instance.
--
Brent Royal-Gordon
Architechies
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