Showing posts with label nil. Show all posts
Showing posts with label nil. Show all posts

Saturday, January 27, 2018

Catching nil as Error

Github gist.

I've posted this as an answer on stackoverflow before, and the information was highly appreciated by some people. The question was like: “How to catch any error, specially unexpectedly found nil in Swift?" Though the author was asking about catching system errors, I decided to post my super-handy Unwrap Snippet there.
struct UnwrapError: Error, CustomStringConvertible { let optional: T? public var description: String { return "Found nil while unwrapping \(String(describing: optional))!" } } public func unwrap(_ optional: T?) throws -> T { if let real = optional { return real } else { throw UnwrapError(optional: optional) } }
The idea of this approach is to replace multiple if let and guard let statements with a single do-try-catch block. You can:
do { // Parse JSON and assign variables which were defined somewhere above let dictionary = try unwrap(JSONSerialization.jsonObject( with: data, options: .allowFragments) as? [String: Any]) isAdsEnabled = try unwrap(dictionary["isAdsEnabled"] as? Bool) // While calling function which require a non-optional parameter in one line of code imageView.image = try UIImage(data: unwrap(receivedData)) // And also you can simplify the building of multipart data var data = Data() data += try unwrap( .utf8)) data += someContent data += try unwrap("\r\n".data(using: .utf8)) } catch error { // Handle error // ... // and exit return nil }
Those who make apps with web backend will definitely like.

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