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November 27, 2017 15:23
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Loan Pattern in Swift
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/// See also | |
/// - http://www.ne.jp/asahi/hishidama/home/tech/scala/sample/using.html | |
/// - https://qiita.com/piyo7/items/c9be1f39bcfea43a778a | |
protocol Closer { | |
func close() | |
} | |
struct Loan { | |
@discardableResult | |
static func using<T: Closer, U>(resource: T, process: (T) throws -> U) -> U? { | |
defer { resource.close() } | |
do { | |
return try process(resource) | |
} catch { | |
print("error: \(error)") | |
return nil | |
} | |
} | |
} | |
/// ex.1 | |
enum MyError: Error { | |
case hoge(String) | |
} | |
class Source: Closer { | |
func read(string: String) throws -> Int { | |
if let number = Int(string) { | |
return number | |
} else { | |
throw MyError.hoge("整数で入力して下さい") | |
} | |
} | |
func close() { | |
print("close") | |
} | |
} | |
let source = Source() | |
Loan.using(resource: source) { try $0.read(string: "123a") } | |
// error: hoge("整数で入力して下さい") | |
// close | |
/// ex.2 | |
class Indicator: Closer { | |
func show() { | |
print("show") | |
} | |
func dismiss() { | |
print("dismiss") | |
} | |
func close() { | |
dismiss() | |
} | |
} | |
let indicator = Indicator() | |
Loan.using(resource: indicator) { $0.show() } | |
// show | |
// dismiss |
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