---
title: fileResourceIdentifierKey
framework: foundation
role: symbol
role_heading: Type Property
path: foundation/urlresourcekey/fileresourceidentifierkey
---

# fileResourceIdentifierKey

The key for the resource’s unique identifier.

## Declaration

```swift
static let fileResourceIdentifierKey: URLResourceKey
```

## Discussion

Discussion The system returns the read-only value as an id. You can use this identifier to determine equality between file system resources with the isEqual(_:) method. Two resources are equal if they have the same file-system path or if their paths link to the same inode on the same file system. The value of this identifier isn’t persistent across system restarts.

## See Also

### File keys

- [fileAllocatedSizeKey](foundation/urlresourcekey/fileallocatedsizekey.md)
- [fileProtectionKey](foundation/urlresourcekey/fileprotectionkey.md)
- [URLFileProtection](foundation/urlfileprotection.md)
- [fileContentIdentifierKey](foundation/urlresourcekey/filecontentidentifierkey.md)
- [fileResourceTypeKey](foundation/urlresourcekey/fileresourcetypekey.md)
- [URLFileResourceType](foundation/urlfileresourcetype.md)
- [fileSecurityKey](foundation/urlresourcekey/filesecuritykey.md)
- [fileSizeKey](foundation/urlresourcekey/filesizekey.md)
- [isAliasFileKey](foundation/urlresourcekey/isaliasfilekey.md)
- [isPackageKey](foundation/urlresourcekey/ispackagekey.md)
- [isRegularFileKey](foundation/urlresourcekey/isregularfilekey.md)
- [isPurgeableKey](foundation/urlresourcekey/ispurgeablekey.md)
- [isSparseKey](foundation/urlresourcekey/issparsekey.md)
- [mayHaveExtendedAttributesKey](foundation/urlresourcekey/mayhaveextendedattributeskey.md)
- [mayShareFileContentKey](foundation/urlresourcekey/maysharefilecontentkey.md)