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# index(_:offsetBy:)

Returns an index that is the specified distance from the given index.

```
func index(_ index: Int, offsetBy n: Int) -> Int
```

## Parameters

`index`

A valid index of the array.

`n`

The distance by which to offset `index`.

## Return Value

An index offset by distance from `index`. If `n` is positive,
this is the same value as the result of `n` calls to `index(after:)`.
If `n` is negative, this is the same value as the result of `abs(n)`
calls to `index(before:)`.

## Discussion

The value passed as `n` must not offset `index` beyond the bounds of the
array.

> Note: To improve performance, this method does not validate that the
> given index is valid before offseting it. Index validation is
> deferred until the resulting index is used to access an element.
> This optimization may be removed in future versions; do not rely on it.

> Complexity: O(1)

---

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