Equatable code generator

Suppose you have a struct in your Swift app like this:

struct Person {
    let firstName: String
    let lastName: String
    let birthday: Date
    let inchesTall: Int
}

In order to allow Person instances to be compared for equality, using the == operator, the struct must adopt Swift's Equatable protocol.

// This doesn't work unless Person adopts the Equatable protocol.
let areSamePerson = (person1 == person2)

Writing code to check if two things are the same is boring, so make your computer do it!

// This prints Equatable protocol code for the Person struct.
adoptEquatable(person)

The adoptEquatable function prints this to the console in Xcode…

extension Person: Equatable {
    public static func ==(lhs: Person, rhs: Person) -> Bool {
        guard lhs.firstName == rhs.firstName else { return false }
        guard lhs.lastName == rhs.lastName else { return false }
        guard lhs.birthday == rhs.birthday else { return false }
        guard lhs.inchesTall == rhs.inchesTall else { return false }
        return true
    }
}

Simply copy that code, paste it into your project, and you're done. 🙌

Use it while debugging

Once you've added adoptEquatable to your project you can also call it while debugging, via the po command.

That's handy!

Show me the code

Feel free to copy this function into your project and start using it.

import Foundation

// Generates code for a class or struct instance to conform to the Equatable protocol.
public func adoptEquatable(_ subject: Any) {
    let mirror = Mirror(reflecting: subject)
    
    let typeName: String = {
        let fullTypeName = String(reflecting: mirror.subjectType)
        let typeNameParts = fullTypeName.components(separatedBy: ".")
        let hasModulePrefix = typeNameParts.count > 1
        return hasModulePrefix
            ? typeNameParts.dropFirst().joined(separator: ".")
            : fullTypeName
    }()
    
    let propertyNames = mirror.children.map { $0.label ?? "" }
    
    // Associate an indentation level with each snippet of code.
    typealias TemplateGroup = [(Int, String)]
    let templateGroups: [TemplateGroup] = [
        [(0, "extension \(typeName): Equatable {")],
        [(1, "public static func ==(lhs: \(typeName), rhs: \(typeName)) -> Bool {")],
        propertyNames.map { (2, "guard lhs.\($0) == rhs.\($0) else { return false }") },
        [(2, "return true")],
        [(1, "}")],
        [(0, "}")]
    ]
    
    // Apply indentation to each line of code while flattening the list.
    let indent = "    "
    let linesOfCode = templateGroups.flatMap { templateGroup -> [String] in
        return templateGroup.map { (indentLevel: Int, code: String) -> String in
            let indentation = String(repeating: indent, count: indentLevel)
            return "\(indentation)\(code)"
        }
    }
    
    let sourceCode = linesOfCode.joined(separator: "\n")
    print(sourceCode)
}

This repository also includes an Xcode playground if you want to experiment.