---
title: base
framework: swift
role: symbol
role_heading: Instance Property
path: swift/reversedcollection/index/base
---

# base

The position after this position in the underlying collection.

## Declaration

```swift
let base: Base.Index
```

## Discussion

Discussion To find the position that corresponds with this index in the original, underlying collection, use that collection’s index(before:) method with the base property. The following example declares a function that returns the index of the last even number in the passed array, if one is found. First, the function finds the position of the last even number as a ReversedIndex in a reversed view of the array of numbers. Next, the function calls the array’s index(before:) method to return the correct position in the passed array. func indexOfLastEven(_ numbers: [Int]) -> Int? {     let reversedNumbers = numbers.reversed()     guard let i = reversedNumbers.firstIndex(where: { $0 % 2 == 0 })         else { return nil }

return numbers.index(before: i.base) }

let numbers = [10, 20, 13, 19, 30, 52, 17, 40, 51] if let lastEven = indexOfLastEven(numbers) {     print("Last even number: \(numbers[lastEven])") } // Prints "Last even number: 40"