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# Observable

A type that emits notifications to observers when underlying data changes.

```
protocol Observable
```

## Overview

Conforming to this protocol signals to other APIs that the type supports
observation. However, applying the `Observable` protocol by itself to a
type doesn’t add observation functionality to the type. Instead, always use
the [`Observable()`](/documentation/Observation/Observable()) macro when adding observation
support to a type.

---

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