---
title: extension
framework: system
role: symbol
role_heading: Instance Property
path: system/filepath/extension
---

# extension

The extension of the file or directory last component.

## Declaration

```swift
var `extension`: String? { get set }
```

## Discussion

Discussion If lastComponent is nil or one of the special path components . or .., get returns nil and set does nothing. If lastComponent does not contain a . anywhere, or only at the start, get returns nil and set will append a . and newValue to lastComponent. Otherwise get returns everything after the last . and set will replace the extension. Examples: /tmp/foo.txt                  => txt /Applications/Foo.app/        => app /Applications/Foo.app/bar.txt => txt /tmp/foo.tar.gz               => gz /tmp/.hidden                  => nil /tmp/.hidden.                 => "" /tmp/..                       => nil Example: var path = "/tmp/file" path.extension = "txt" // path is "/tmp/file.txt" path.extension = "o"   // path is "/tmp/file.o" path.extension = nil    // path is "/tmp/file" path.extension = ""     // path is "/tmp/file."