When an Array has an Element type that is an optional, I'd like to count the non-nil elems. Is there a way to do this with just a var? How can I say that Element is an Optional<T>, without introducing T via the generic func? Thanx.
extension Array {
func someCount<T>() -> Int where Element == Optional<T> {
self.reduce(0) { count, elem in count + (elem == nil ? 0 : 1)
}
}
I found the very clever ideas here, and could make it work…
https://stackoverflow.com/questions/25064644/how-to-determine-if-a-generic-is-an-optional-in-swift
protocol OptionalType {
associatedtype Wrapped
func map<U>(_ f: (Wrapped) throws -> U) rethrows -> U?
}
extension Optional: OptionalType {}
extension Sequence where Iterator.Element: OptionalType {
private func removeNils() -> [Iterator.Element.Wrapped] {
var result: [Iterator.Element.Wrapped] = []
for element in self {
if let element = element.map({ $0 }) {
result.append(element)
}
}
return result
}
var total : Int {
self.removeNils().count
}
}
let ar : [Int?] = [1, 2, nil, 4]
print(ar.total)
Or specifically the Array extension:
protocol OptionalType {
associatedtype Wrapped
func map<U>(_ f: (Wrapped) throws -> U) rethrows -> U?
}
extension Optional: OptionalType {}
extension Array where Element: OptionalType {
private func removeNils() -> [Element.Wrapped] {
var result: [Element.Wrapped] = []
for element in self {
if let element = element.map({ $0 }) {
result.append(element)
}
}
return result
}
var total : Int {
self.removeNils().count
}
}
let ar : [Int?] = [1, 2, nil, 4]
print(ar.total)
Thanx - that is a clever sidestep in order to get a protocol for Optional other than "must be enum with cases none and some", but in practice I'll just keep typing my extra two parens after .someCount :-)
Yes, using func is much easier. But your question was a challenge to find a way to express it as a var. Good continuation, don't forget to close the thread. It may be of interest of others to see there was a solution tou the question, even though too complex for the benefit.
