أنواع Result — ‏Result<T, Error>

لماذا Result؟

إنشاء Result

enum ParseError: Error { case badInt }
func parseInt(_ s: String) -> Result<Int, Error> {
    if let n = Int(s) { return .success(n) }
    else { return .failure(ParseError.badInt) }
}
print(parseInt("42"))
print(parseInt("nope"))

استخدام switch مع Result

let r = parseInt("10")
switch r {
case .success(let n): print("number =", n)
case .failure(let e): print("error:", e)
}

تحويل Results

let r1 = parseInt("5").map { $0 * 2 }              // Result<Int, Error>
let r2 = parseInt("x").map { $0 * 2 }                    // still .failure
let r3 = parseInt("8").flatMap { n in                    // chain Results
    n % 2 == 0 ? .success(n/2) : .failure(ParseError.badInt)
}
let rErr = parseInt("x").mapError { $0 }                 // transform error type if needed
print(r1, r2, r3, rErr)

Throws ← Result

enum LoadError: Error { case notFound }
func load(text name: String) throws -> String {
    guard name == "ok" else { throw LoadError.notFound }
    return "loaded"
}
// Build a Result from a throwing call:
let res = Result { try load(text: "ok") }     // .success("loaded")
let res2 = Result { try load(text: "missing") } // .failure(LoadError.notFound)
print(res, res2)

Result ← throws

let outcome = parseInt("12")
do {
    let value = try outcome.get()   // throws if .failure
    print("value =", value)
} catch {
    print("thrown from get():", error)
}

معنى Result

مراجعة