# swift-case-paths **Repository Path**: BitBuilder/swift-case-paths ## Basic Information - **Project Name**: swift-case-paths - **Description**: https://github.com/pointfreeco/swift-case-paths - **Primary Language**: Unknown - **License**: MIT - **Default Branch**: main - **Homepage**: None - **GVP Project**: No ## Statistics - **Stars**: 0 - **Forks**: 0 - **Created**: 2022-08-03 - **Last Updated**: 2022-08-05 ## Categories & Tags **Categories**: Uncategorized **Tags**: None ## README # 🧰 CasePaths [![CI](https://github.com/pointfreeco/swift-case-paths/workflows/CI/badge.svg)](https://actions-badge.atrox.dev/pointfreeco/swift-case-paths/goto) [![](https://img.shields.io/endpoint?url=https%3A%2F%2Fswiftpackageindex.com%2Fapi%2Fpackages%2Fpointfreeco%2Fswift-case-paths%2Fbadge%3Ftype%3Dswift-versions)](https://swiftpackageindex.com/pointfreeco/swift-case-paths) [![](https://img.shields.io/endpoint?url=https%3A%2F%2Fswiftpackageindex.com%2Fapi%2Fpackages%2Fpointfreeco%2Fswift-case-paths%2Fbadge%3Ftype%3Dplatforms)](https://swiftpackageindex.com/pointfreeco/swift-case-paths) Case paths bring the power and ergonomics of key paths to enums! ## Motivation Swift endows every struct and class property with a [key path](https://developer.apple.com/documentation/swift/swift_standard_library/key-path_expressions). ``` swift struct User { var id: Int var name: String } \User.id // WritableKeyPath \User.name // WritableKeyPath ``` This is compiler-generated code that can be used to abstractly zoom in on part of a structure, inspect and even change it, while propagating these changes to the structure's whole. They unlock the ability to do many things, like [key-value observing](https://developer.apple.com/documentation/swift/cocoa_design_patterns/using_key-value_observing_in_swift) and [reactive bindings](https://developer.apple.com/documentation/combine/receiving_and_handling_events_with_combine), [dynamic member lookup](https://github.com/apple/swift-evolution/blob/master/proposals/0252-keypath-dynamic-member-lookup.md), and scoping changes to the SwiftUI [environment](https://developer.apple.com/documentation/swiftui/environment). Unfortunately, no such structure exists for enum cases! ``` swift enum Authentication { case authenticated(accessToken: String) case unauthenticated } \Authentication.authenticated // 🛑 ``` And so it's impossible to write similar generic algorithms that can zoom in on a particular enum case. ## Introducing: case paths This library intends to bridge this gap by introducing what we call "case paths." Case paths can be constructed simply by prepending the enum type and case name with a _forward_ slash: ``` swift import CasePaths /Authentication.authenticated // CasePath ``` ### Case paths vs. key paths While key paths package up the functionality of getting and setting a value on a root structure, case paths package up the functionality of extracting and embedding a value on a root enumeration. ``` swift user[keyPath: \User.id] = 42 user[keyPath: \User.id] // 42 let authentication = (/Authentication.authenticated).embed("cafebeef") (/Authentication.authenticated).extract(from: authentication) // Optional("cafebeef") ``` Case path extraction can fail and return `nil` because the cases may not match up. ``` swift (/Authentication.authenticated).extract(from: .unauthenticated) // nil ```` Case paths, like key paths, compose. Where key paths use dot-syntax to dive deeper into a structure, case paths use a double-dot syntax: ``` swift \HighScore.user.name // WritableKeyPath /Result..Authentication.authenticated // CasePath, String> ``` Case paths, also like key paths, provide an "[identity](https://github.com/apple/swift-evolution/blob/master/proposals/0227-identity-keypath.md)" path, which is useful for interacting with APIs that use key paths and case paths but you want to work with entire structure. ``` swift \User.self // WritableKeyPath /Authentication.self // CasePath ``` Key paths are created for every property, even computed ones, so what is the equivalent for case paths? Well, "computed" case paths can be created by providing custom `embed` and `extract` functions: ``` swift CasePath( embed: { decryptedToken in Authentication.authenticated(token: encrypt(decryptedToken)) }, extract: { authentication in guard case let .authenticated(encryptedToken) = authentication, let decryptedToken = decrypt(token) else { return nil } return decryptedToken } ) ``` Since Swift 5.2, key path expressions can be passed directly to methods like `map`. The same is true of case path expressions, which can be passed to methods like `compactMap`: ``` swift users.map(\User.name) authentications.compactMap(/Authentication.authenticated) ``` ## Ergonomic associated value access CasePaths uses Swift reflection to automatically embed and extract associated values from _any_ enum in a single, short expression. This helpful utility is made available as a public module function that can be used in your own libraries and apps: ``` swift (/Authentication.authenticated).extract(from: .authenticated("cafebeef")) // Optional("cafebeef") ``` ## Installation You can add CasePaths to an Xcode project by adding it as a package dependency. > https://github.com/pointfreeco/swift-case-paths If you want to use CasePaths in a [SwiftPM](https://swift.org/package-manager/) project, it's as simple as adding a `dependencies` clause to your `Package.swift`: ``` swift dependencies: [ .package(url: "https://github.com/pointfreeco/swift-case-paths.git", from: "0.4.0") ] ``` ## Documentation The latest documentation for CasePaths' APIs is available [here](https://pointfreeco.github.io/swift-case-paths/). ## Other libraries - [`EnumKit`](https://github.com/gringoireDM/EnumKit) is a protocol-oriented, reflection-based solution to ergonomic enum access and inspired the creation of this library. ## Interested in learning more? These concepts (and more) are explored thoroughly in [Point-Free](https://www.pointfree.co), a video series exploring functional programming and Swift hosted by [Brandon Williams](https://github.com/mbrandonw) and [Stephen Celis](https://github.com/stephencelis). The design of this library was explored in the following [Point-Free](https://www.pointfree.co) episodes: - [Episode 87](https://www.pointfree.co/episodes/ep87-the-case-for-case-paths-introduction): The Case for Case Paths: Introduction - [Episode 88](https://www.pointfree.co/episodes/ep88-the-case-for-case-paths-properties): The Case for Case Paths: Properties - [Episode 89](https://www.pointfree.co/episodes/ep89-case-paths-for-free): Case Paths for Free video poster image ## License All modules are released under the MIT license. See [LICENSE](LICENSE) for details.