Type Safe Identifiers with automatic conformance to Identifiable

identifier.swift

/// This was inspired by this... https://www.swiftbysundell.com/articles/type-safe-identifiers-in-swift/
/// I wanted to try and find a way to have a type safe identifier that also allowed conformance to Identifiable

import Foundation

struct Identifier<Subject: Identified>: Hashable {
	let value: Subject.IdentifierType

	init(_ value: Subject.IdentifierType) {
		self.value = value
	}
}

extension Identifier: CustomStringConvertible {
	public var description: String {
		"\(value)"
	}
}

extension Identifier: ExpressibleByStringLiteral, ExpressibleByUnicodeScalarLiteral, ExpressibleByExtendedGraphemeClusterLiteral where Subject.IdentifierType == String {
	init(stringLiteral value: String) {
		self.value = value
	}

	init(unicodeScalarLiteral value: String) {
		self.value = value
	}

	init(extendedGraphemeClusterLiteral value: String) {
		self.value = value
	}
}

extension Identifier: ExpressibleByIntegerLiteral where Subject.IdentifierType == Int {
	init(integerLiteral value: Int) {
		self.value = value
	}
}

protocol Identified: Identifiable {
	associatedtype IdentifierType: Hashable

	var identifier: Identifier<Self> { get }
}

extension Identified {
	var id: IdentifierType {
		identifier.value
	}
}

struct Person: Identified {
	typealias IdentifierType = String

	let identifier: Identifier<Self>
}

let person = Person(identifier: "3")

dump(person)
print(person.identifier)
print(person.id) // id comes "for free" from the automatic Identifiable conformance.

let person2 = Person(identifier: "5")

dump(person2)
print(person2.identifier)
print(person2.id)

let randomIdentifier: Identifier<Person> = 3 // Error because Identifier<Person> requires a String
print(randomIdentifier)

struct Account: Identified {
	typealias IdentifierType = String

	let identifier: Identifier<Self>
}

let account = Account(identifier: "Account1")

func doSomething(personID: Identifier<Person>) {
	print("Hello, \(personID)")
}

doSomething(personID: person.identifier)
doSomething(personID: account.identifier) // Error because Identifier<Account> and Identifier<Person> are not compatible.