---
title: Foundation Data Types
framework: foundation
role: collectionGroup
role_heading: API Collection
path: foundation/foundation-data-types
---

# Foundation Data Types

This document describes the data types and constants found in the Foundation framework.

## Topics

### Classes

- [NSKeyValueObservation](foundation/nskeyvalueobservation.md)
- [NSKeyValueSharedObservers](foundation/nskeyvaluesharedobservers.md)
- [NSKeyValueSharedObserversSnapshot](foundation/nskeyvaluesharedobserverssnapshot.md)

### Protocols

- [DiscreteFormatStyle](foundation/discreteformatstyle.md)
- [NSKeyValueObservingCustomization](foundation/nskeyvalueobservingcustomization.md)

### Structures

- [AsyncCharacterSequence](foundation/asynccharactersequence.md)
- [AsyncLineSequence](foundation/asynclinesequence.md)
- [AsyncUnicodeScalarSequence](foundation/asyncunicodescalarsequence.md)
- [Expression](foundation/expression.md)
- [NSAttributedStringFormattingContextKey](foundation/nsattributedstringformattingcontextkey.md)
- [NSKeyValueChangeKey](foundation/nskeyvaluechangekey.md)
- [NSKeyValueObservedChange](foundation/nskeyvalueobservedchange.md)
- [NSKeyValueOperator](foundation/nskeyvalueoperator.md)
- [PresentationIntent](foundation/presentationintent.md)

### Variables

- [NSOperationNotSupportedForKeyException](foundation/nsoperationnotsupportedforkeyexception.md)
- [NSURLSessionUploadTaskResumeData](foundation/nsurlsessionuploadtaskresumedata.md)
- [kCFStringEncodingASCII](foundation/kcfstringencodingascii.md)

### Macros

- [Expression(_:)](foundation/expression(_:).md)
- [Predicate(_:)](foundation/predicate(_:).md)

### Type Aliases

- [uuid_string_t](foundation/uuid_string_t.md)
- [uuid_t](foundation/uuid_t.md)

## See Also

### Reference

- [Foundation Enumerations](foundation/foundation-enumerations.md)