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

[Charles Srstka]

I’ll take the opposite stance. Why limit this to initialization? I’d love to be able to guard assignments to *any* variable, whether it’s a property or not:

func foo() {
	let bar: String

	if someCondition {
		guard bar = mightReturnOptional() else {
			return
		}
	} else {
		bar = wontReturnOptional()
	}

	self.doSomethingWith(bar)
}

As opposed to:

func foo() {
	let bar: String

	if someCondition {
		guard let _bar = mightReturnOptional() else {
			return
		}

		bar = _bar
	} else {
		bar = wontReturnOptional()
	}

	self.doSomethingWith(bar)
}

Charles

> On Jul 25, 2017, at 4:13 PM, Niels Andriesse via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Although I have come across this problem as well (particularly when initializing from JSON), I don't think the solution is to fundamentally change initialization behavior like this, because 1. ) that is probably going to break a good deal of existing code and 2. ) I think that the introduction of the Codable protocol in Swift 4 will eliminate most cases where this is really a problem.
> On Wed, 26 Jul 2017 at 02:30 Taylor Swift via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> I’d be in favor of this.
> 
> On Tue, Jul 25, 2017 at 5:44 AM, philohan95 via swift-evolution <swift-evolution at swift.org <mailto: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
> }
> ```
> 
> As you can see we had to use the properties twice (this would also be the case of `if let`) making the initializer twice as long as necessary and becomes a pain to implement when having more than 1 property.
> 
> My idea is extending the power of the `guard` statement
> 
> Idea:
>         init?(data: [String: Any]) {
>                 guard
>                         someProperty = data["some_key"], // Currently fails because `self` us used before all stored properties are initialized
>                         anotherProperty = data["another_key"]
>                 else {
>                         return nil
>                 }
>         }
> }
> 
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