[swift-evolution] Idea: Properties in Failable Initializers less verbose

[Robert Bennett]

Is there a reason that a throwing unwrap function/operator isn’t part of the standard library? Seems like it would be handy to be able to have a one-liner for attempting to unwrap and throw if it’s nil. Something like


postfix operator .?!

extension Optional {
	static postfix func .?!(optional: Optional<Wrapped>) throws -> Wrapped {
		switch optional {
		case let .some(wrapped):
			return wrapped
		case .none:
			throw UnwrapError()
		}
	}
}

init?(data: [String: Any]) {
	do {
		self.someProperty = try data["some_key”].?!
		self.anotherProperty = try data["another_key”].?!
	} catch is UnwrapError {
		return nil
	}
}


> On Jul 26, 2017, at 12:13 PM, Chris Lattner via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
>> On Jul 25, 2017, at 2:44 AM, philohan95 via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> I think the current way to initiate models in a Failable Initializer `init?()` is overly verbose and should be shortened down so less boilerplate should be needed.
>> 
>> The current way:
>> 
>> ```
>> let someProperty: Any
>> let anotherProperty: Any
>> 
>> init?(data: [String: Any]) {
>> 	guard
>> 		let someProperty = data["some_key"],
>> 		let anotherProperty = data["another_key"]
>> 	else {
>> 		return nil
>> 	}
>> 
>> 	self. someProperty = someProperty
>> 	self. anotherProperty = anotherProperty
>> }
>> ```
> 
> Guard isn’t really the right answer for this, I’d try something like this (where unwrapOrThrow is the obvious generic function you can define yourself):
> 
> init?(data: [String: Any]) {
> 	do {
> 		self.someProperty = try unwrapOrThrow(data["some_key”])
> 		self.anotherProperty = try unwrapOrThrow(data["another_key”])
> 	} catch {
> 		return nil
> 	}
> }
> 
> -Chris
> 
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