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# index(of:)

Returns the lowest index whose corresponding array value is equal to a given object.

```
func index(of anObject: Any) -> Int
```

## Parameters

`anObject`

An object.

## Return Value

The lowest index whose corresponding array value is equal to `anObject`. If none of the objects in the array is equal to `anObject`, returns `NSNotFound`.

## Discussion

Starting at index `0`, each element of the array is passed as an argument to an <doc://com.apple.documentation/documentation/ObjectiveC/NSObjectProtocol/isEqual(_:)> message sent to `anObject` until a match is found or the end of the array is reached. Objects are considered equal if <doc://com.apple.documentation/documentation/ObjectiveC/NSObjectProtocol/isEqual(_:)> (declared in the <doc://com.apple.documentation/documentation/ObjectiveC/NSObjectProtocol> protocol) returns <doc://com.apple.documentation/documentation/Swift/true>.

## See Also

[`-  containsObject:`](/documentation/Foundation/NSArray/contains(_:))

Returns a Boolean value that indicates whether a given object is present in the array.


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