Zip function.
Zip function is defined on sequences in Swift. This is a nice extension to have it on Optional.
Let say you have some computations or values that are optional. It might be tedious to if let them. Using zip you just flip the container inside out (check out how type is transformed in this documentation on zip in haskell) and map on the result.
let userName: String?
let userLast: String?
let userAge: Int?
zip(userName, userLast, userAge)
.map{ (name: String, last: String, age: Int) in
// Working with not optional values
}Allaws for calling multiple async functions concurently to get tuple of results.
let (name, age) = await asyncZip(
await asyncGetUserName(),
await asyncGetUserAge()
)
let user = User(name: name, age: age)The same as asyncZip but the last argument is a function that can transform this tuple into a instance of some type.
struct User {
let name: String
let age: Int
}
let user: User = asyncZip(
await asyncGetUserName(),
await asyncGetUserAge(),
with: User.init
)In this example you can just write User.init as the compiler will match to the correct function. But you can use a closure together with trailing syntax to do whatever you need.
struct User {
let name: String
let age: Int
}
let user: User = asyncZip(
await asyncGetUserName(),
await asyncGetUserAge()
) { (fetchedName: String, fetchedAge: Int) in
User(name: fetchedName, age: fetchedAge)
}zipand zipWith on Either
Either is a more general type than Optional or Result and it also has the zip function defined for it (as it has map). If you want to see more about Either then check this respository: EitherSwift Swift Package
let userName: Either<Int,String> = getUserNameOrErrorCode()
let userLastName: Either<Int,String> = getUserLastNameOrErrorCode()
zip(userName, userLastName)
.map { (name: String, last: String) in
// When all are .right cases then you have the values here
}Many times you run your code to do smething with values that are returned. To stramline that you can pass a function to zipWith.
func validateName (_ s: String) -> Either<Int,String> { ... }
func validateLastName(_ s: String) -> Either<Int,String> { ... }
struct User { let name: String; let lastName: String }
// Given two Eithers when they both are right then returns User.
// Notice as this also returns an Either but luckely this type has a map.
let createUserWhenValid: Either<Int,String>,Either<Int,String>) -> Either<Int,User> = zip(with: User.init)
createUserWhenValid(validateName, validateLastName)
.map { (user: User) in
// Real instance of User type 😎
}
.mapLeft { (errorCodes: [Int]) in
// error codes that were returned as left values
}If you want to streamline working with Optionals in Swift then please checkout OptionalAPI Swift Package. It has rich documentation and tests to show how it can be used.
This project is part of the 🐇🕳 Rabbit Hole Packages Collection