# fileID() Produces a unique identifier for the source file in which the macro appears. ``` @freestanding(expression) macro fileID() -> T where T : ExpressibleByStringLiteral ``` ## Overview The unique identifier has the form *module*/*file*, where *file* is the name of the file in which the expression appears and *module* is the name of the module that this file is part of. Because `#fileID` doesn’t embed the full path to the source file, unlike `#filePath`, it gives you better privacy and reduces the size of the compiled binary. Note: To parse a `#fileID` expression, read the module name as the text before the first slash (`/`) and the filename as the text after the last slash. In future versions of Swift, the string might contain multiple slashes, such as `MyModule/some/disambiguation/MyFile.swift`. This macro’s value can be changed by `#sourceLocation`, as described in [Line Control Statement](https://docs.swift.org/swift-book/documentation/the-swift-programming-language/statements#Line-Control-Statement) in [The Swift Programming Language](https://docs.swift.org/swift-book/). --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)