CustomHigherOrderFunctions.swift

// Custom Implementation of higher order functions: map, filter, reduce

extension Collection {
    func customMap<T>(_ tranform: (Element) -> T) -> [T] {
        var result = [T]()

        for element in self {
            result.append(tranform(element))
        }

        return result
    }

    func customFilter(_ isIncluded: (Element) -> Bool) -> [Element] {
        var result = [Element]()

        for element in self {
            if isIncluded(element) {
                result.append(element)
            }
        }

        return result
    }

    func customReduce<Result>(initialResult: Result, nextPartialResult: (Result, Element) -> Result) -> Result {
        var result = initialResult

        forEach { element in
            result = nextPartialResult(result, element)
        }

        return result
    }
}