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# Undefined Components

Constants that denote that the value of a date component is undefined.

## Discussion

For example, when an [`NSDateComponents`](/documentation/Foundation/NSDateComponents) object is created as the result of calculating the distance in time between two dates represented by a particular calendar, the value for the [`weekOfYear`](/documentation/Foundation/NSCalendar/Unit/weekOfYear) component would be set to [`NSDateComponentUndefined`](/documentation/Foundation/NSDateComponentUndefined).

## Topics

### Constants

[`var NSDateComponentUndefined: Int`](/documentation/Foundation/NSDateComponentUndefined)

Specifies a date component without a value.

[`var NSUndefinedDateComponent: Int`](/documentation/Foundation/NSUndefinedDateComponent)

Specifies a date component without a value.


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