[swift-evolution] Proposal Draft: Optional Upgrading Assignment.

[Paul Ossenbruggen]

Just sugar for that, plus there is symmetry to this proposal, it is more discoverable, and it is more concise.


> On Feb 4, 2016, at 1:57 AM, Taras Zakharko <taras.zakharko at uzh.ch> wrote:
> 
> -1 from me
> 
>   let x = Optional(“Some Value”) 
> 
> does the job just fine, is very clean,  and I don’t see any reason to shorten it. 
> 
> — Taras
> 
> 
>> On 04 Feb 2016, at 10:33, Allen Ding via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> On Thu, Feb 4, 2016 at 4:28 PM, Paul Ossenbruggen via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> Draft Proposal feedback welcome.
>> 
>> ## Introduction
>> 
>> Currently to make a optional from a value the type name must be repeated:
>> 
>> 	let x = “Some Value”
>> 	let y : String? = x
>> 
>> This takes away some of the advantage of type inference because the very next line I must specify the type.
>> 
>> Any use case examples? I've been trying to figure out why is this needs fixing (I don't even see it as a problem).
>> 
>> 
>> ## Proposal
>> 
>> I propose the following syntax:
>> 
>> 	let y? = x
>> 
>> This binds a new optional y which wraps the same value of x. It follows the same conventions as var and let that currently exist in the language. 
>> 
>> The advantages: this is easier to read, more compact, and lets type inference determine the type. 
>> 
>> If let and other conditionals would not support this syntax and optionals of optionals is not supported. So let x?? = y would not result in an optional optional. Also if y was an optional it would not let you upgrade that.
>> 
>> ## Detailed Design
>> 
>> The grammar: 
>> 
>> 	let optionalValue? = value
>> 
>> This would not make sense in the if let, (guard let) context because if let unwraps the value, so this would be an error. 
>> 
>> This should not conflict with pattern matching as that requires the case keyword. 
>> 
>> Wrapping optional in an optional is an error. 
>> 
>> ## Impact on existing code
>> 
>> The current syntax will continue to exist so it will have no impact on existing code. 
>> 
>> ## Alternatives Considered
>> 
>> None. 
>> 
>> 
>> 
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