How do I tell which guard statement failed?

Question

If I’ve got a bunch of chained guard let statements, how can I diagnose which condition failed, short of breaking apart my guard let into multiple statements?

Given

Answer 1

My two cents:
Since Swift doesn't let me add the where in the guard let, I came up with this solution instead:

func validate<T>(_ input: T?, file: String = #file, line: Int = #line) -> T? {
    guard let input = input else {
        print("Nil argument at \(file), line: \(line)")
        return nil
    }
    return input
}


class Model {
    let id: Int
    let name: String
    
    init?(id: Int?, name: String?) {
        guard let id = validate(id),
            let name = validate(name) else {
            return nil
        }
        self.id = id
        self.name = name
    }
}

let t = Model(id: 0, name: "ok") // Not nil
let t2 = Model(id: 0, name: nil) // Nil
let t3 = Model(id: nil, name: "ok") // Nil