要素と位置(idx)をペアにしたコレクションを返す

Sequence+.swift

import Foundation

extension Sequence {
    
    func filterNot(_ isExcluded: (Self.Iterator.Element) throws -> Bool) rethrows -> [Self.Iterator.Element] {
        var res: [Self.Iterator.Element] = []
        for e in self where try !isExcluded(e) {
            res.append(e)
        }
        return res
    }
    
    func zipWithIndex() -> Zip2Sequence<Self, CountableClosedRange<Int>> {
        return zip(self, 0...Int.max)
    }
}

let ary = Array(10...20)
let predicate = { (n1: Int, n2: Int) -> Bool in n1 % 2 == 0 }
let res = ary.zipWithIndex().filterNot(predicate)
print(res) // [(11, 1), (13, 3), (15, 5), (17, 7), (19, 9)]