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

[Dan Raviv]

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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> swift-evolution at swift.org
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>
>
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