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# index(before:)

Returns the position immediately before the given index.

```
func index(before index: Int) -> Int
```

## Parameters

`index`

A valid index of the array. `i` must be greater
than `startIndex`.

## Return Value

The index immediately preceding `i`.

## Discussion> Note: To improve performance, this method does not validate that the
> index is valid before decrementing 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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