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# init(forReadingWith:)

Returns an `NSUnarchiver` object initialized to read an archive from a given data object.

```
init?(forReadingWith data: Data)
```

## Parameters

`data`

The archive data.

## Return Value

An `NSUnarchiver` object initialized to read an archive from `data`. Returns `nil` if `data` is not a valid archive.

## Discussion

The method decodes the system version number that was archived in `data` prepares the `NSUnarchiver` object for a subsequent invocation of [`decodeObject()`](/documentation/Foundation/NSCoder/decodeObject()).

Raises an `NSInvalidArgumentException` if `data` is `nil`.

## See Also

  [Archives and Serializations Programming Guide](https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/Archiving/Archiving.html#//apple_ref/doc/uid/10000047i)

[`systemVersion`](/documentation/Foundation/NSUnarchiver/systemVersion-swift.property)

The system version number in effect when the archive was created.


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