Sequence+RecursiveFlatten

Sequence+RecursiveFlatten.swift

extension Sequence {
    
    func recursiveFlatten(_ childSelector: (Element) -> [Element]) -> [Element] {
        var output: [Element] = []
        for item in self {
            output.append(item)
            let newItems = childSelector(item)
            if newItems.count > 0 {
                output += newItems.recursiveFlatten(childSelector)
            }
        }
        return output
    }
    
    func recursiveFlatMap<T>(_ transformer: (Element) -> (T, [Element])) -> [T] {
        var output: [T] = []
        for item in self {
            let outItem = transformer(item)
            output.append(outItem.0)
            if outItem.1.count > 0 {
                output += outItem.1.recursiveFlatMap(transformer)
            }
        }
        return output
    }
}