[swift-evolution] allowing to specify optionality with type inference

Maximilian H├╝nenberger m.huenenberger at me.com
Sun Mar 27 14:13:41 CDT 2016


Only to be complete:

let str1 = String?() // nil
let str2 = String?("") // ""

Kind regards
- Maximilian

> Am 24.03.2016 um 11:57 schrieb Hugues Bernet-Rollande via swift-evolution <swift-evolution at swift.org>:
> 
> Hey All,
> 
> I think Andrew already nailed my proposal.
> 
> Thank you all.
> 
> 
> Hugues BERNET-ROLLANDE
> 
> --
> hugues at xdev.fr
> http://www.xdev.fr
> http://www.linkedin.com/in/huguesbr
>> On Mar 24 2016, at 11:56 am, Dan Raviv <dan.raviv at gmail.com> wrote: 
>> Hi Hughes,
>> 
>> What's wrong with:
>> let s = Optional(String("abc"))
>> 
>> 
>> On Thu, Mar 24, 2016 at 12:22 PM, Hugues Bernet-Rollande via swift-evolution <swift-evolution at swift.org> wrote:
>> In a strongly typed language, such as Swift is, type inference is greatly appreciated as it declutter the instance type definition.
>> 
>> For example, in the following statement, the compiler easily deduct the type of `aString` by the return type of `String.init()`
>> 
>> ```
>> let aString = String()
>> ```
>> 
>> Optional are generic enum which can contain a value of a generic type or nil (https://github.com/apple/swift/blob/master/stdlib/public/core/Optional.swift)
>> 
>> Sometime you may want specify that the instance is of type optional in which even if you are a the same time assigning a value to this instance.
>> In which case you loose the type inference mechanism and you have to define both (the optionality as well as the type). 
>> For example, you may want specify an optional String with a default value.
>> 
>> ```
>> var a:String? = String()
>> // or
>> var b = String() as String?
>> // or
>> var c:Optional<String> = String()
>> ```
>> 
>> But the compiler can already infer the variable type from this assignment, it just miss the "optionality" of the variable.
>> It would be nice to be able to express this.
>> 
>> Then for, I propose the following syntax evolution:
>> 
>> ```
>> var a:? = String()
>> // and/or (not recommended because more prone to typo and unclear...)
>> var a = String() as?
>> ```
>> 
>> This would allow for more synthetic optional declaration.
>> 
>> I've draft a proposal on my `swift-evolution` fork:
>> 	https://github.com/huguesbr/swift-evolution/blob/optionality-type-with-type-inference/proposals/0057-optionality-type-with-type-inference.md
>> 
>> Let me know what you think.
>> 
>> 
>> Hugues BERNET-ROLLANDE
>> 
>> --
>> hugues at xdev.fr
>> http://www.xdev.fr
>> http://www.linkedin.com/in/huguesbr
>> 
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