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

[Félix Cloutier]

Second option: use `let y = Optional(x)`.

Félix

> Le 4 févr. 2016 à 03:28:09, Paul Ossenbruggen via swift-evolution <swift-evolution at swift.org> a écrit :
> 
> 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.
> 
> ## 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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