I want to write function that walk through array and return indexes where that element was found.
Something like:
extension Array {
func elementIndexes<T>() -> [Int] {
// if element is kind of class "T" add it to array [T] and then return
}
}
However, I have not succeeded. How can I do that?
It sounds, to clear up the wording, that you want to get all indices where the element is type T. Here's an extension on Array that'll do that, with an example:
extension Array {
func indices<T>(ofType type: T.Type) -> [Int] {
return self.enumerated().filter({ $0.element is T }).map({ $0.offset })
}
}
struct TypeA { }
struct TypeB { }
let list: [Any] = [TypeA(), TypeB(), TypeB(), TypeA()]
print(list.indices(ofType: TypeA.self)) // prints [0, 3]
self.enumerated().flatMap{ $0.element is T ? $0.offset : nil }You can filter the indices directly, this is more generic version (credits to Leo Dabus and Hamish)
extension Collection {
func indices<T>(of type: T.Type) -> [Index] {
return indices.filter { self[$0] is T }
}
}
indices.lazy.filterthis might work for you:
extension Array {
func indices<T>(of: T.Type) -> [Int] {
return self.enumerated().flatMap { $0.element is T ? $0.offset : nil }
}
}
or if you'd like dealing with more traditional solutions then this is your way:
extension Array {
func indices<T>(of: T.Type) -> [Int] {
var indices = [Int]()
for (n, item) in self.enumerated() {
if item is T {
indices.append(n)
}
}
return indices
}
}
like with this test array:
let array: [Any] = [1, 2, "3", "4"]
debugPrint(array.indices(of: String.self))
both presents the the same output in Playground, which is:
[2, 3]
[T]?