filtermap.swift

extension Sequence {
    public func filterMap<T>(map: (Self.Iterator.Element) throws -> (Bool, T)) rethrows -> [T] {
        var array : [T] = []
        for element in self {
            do {
                let (result, value) = try map(element)
                if result {
                    array.append(value)
                }
            }
        }
        return array
    }
    
    public func filterMap<T>(includeElement: (Self.Iterator.Element) throws -> Bool, map: (Self.Iterator.Element) throws -> T) rethrows -> [T] {
        var array : [T] = []
        for element in self {
            do {
                if try includeElement(element) {
                    array.append(try map(element))
                }
            }
        }
        return array
    }
}


print((0...10).filterMap { return ($0 % 2 == 0, $0 * 2) })
// prints [0, 4, 8, 12, 16, 20]

print(
    (0...10).filterMap(
        includeElement: { return $0 % 2 == 0 },
        map: { return $0 * 4 }
    )
)
// prints [0, 8, 16, 24, 32, 40]


print([nil, 1, 4, nil, 6].filterMap(includeElement: { $0 != nil }, map: { $0! + 1 }))
// prints [2, 5, 7]