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# identifier

A unique string identifying the HealthKit object type.

```
var identifier: String { get }
```

## Discussion

Each object type has a unique identifier. The identifiers can be grouped into different categories: [`HKQuantityTypeIdentifier`](/documentation/HealthKit/HKQuantityTypeIdentifier), [`HKCategoryTypeIdentifier`](/documentation/HealthKit/HKCategoryTypeIdentifier), [`HKCharacteristicTypeIdentifier`](/documentation/HealthKit/HKCharacteristicTypeIdentifier), [`HKCorrelationTypeIdentifier`](/documentation/HealthKit/HKCorrelationTypeIdentifier), and [`HKDocumentTypeIdentifier`](/documentation/HealthKit/HKDocumentTypeIdentifier) Each group of identifiers is associated with a different concrete subclass of `HKObjectType`.

---

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