[swift-evolution] [Pitch] Introducing `Unwrappable` protocol

[Erica Sadun]

> On Mar 7, 2017, at 1:31 PM, Jonathan Hull <jhull at gbis.com> wrote:
> 
> Would ‘if let foo = foo’ still be allowed?
> 
> 

Existing code should to continue to work with `if let foo = foo`. I don't
believe I put anything in-text about removing this, but if you see something
let me know.

-- E


>> On Mar 7, 2017, at 12:14 PM, Erica Sadun via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> I have been involved in several separate related draft proposals for discussions 
>> that were cut off about 4 months ago. I believe they meet the criteria for Stage 2,
>> but I'm doing a poor job presenting them coherently on-list.
>> 
>> Because of that, I'm going to start over here, hopefully pulling in all the details
>> and allowing the community to provide feedback and direction. The following 
>> gist is an amalgam of work I was discussing with Xiaodi Wu, Chris Lattner, and
>> David Goodine.
>> 
>> https://gist.github.com/erica/aea6a1c55e9e92f843f92e2b16879b0f <https://gist.github.com/erica/aea6a1c55e9e92f843f92e2b16879b0f>
>> 
>> I've decided to link to the gist rather than paste the entire proposal as that never seems to 
>> really work here.
>> 
>> 
>> In a nutshell:
>> 
>> Unwrapping values is one of the most common Swift tasks and it is unnecessarily complex. 
>> 
>> Consider the following solutions:
>> 
>> Introduce an unwrap keyword for Optional values
>> Introduce an Unwrappable protocol for associated-value enumerations.
>> Apply unwrap to non-Optional values.
>> Extend for and switch.
>> Fix pattern match binding issues.
>> Simplify complex binding.
>>  <https://gist.github.com/erica/aea6a1c55e9e92f843f92e2b16879b0f#motivation>Motivation
>> 
>> Unwrapping with conditional binding and pattern matching is unnecessarily complex and dangerous:
>> 
>> Using "foo = foo" fails DRY principles <https://en.wikipedia.org/wiki/Don%27t_repeat_yourself>. 
>> Using case let .some(foo) = foo or case .some(let foo) = foo fails KISS principles <https://en.wikipedia.org/wiki/KISS_principle>.
>> Using the = operator fails the Principle of Least Astonishment <https://en.wikipedia.org/wiki/Principle_of_least_astonishment>.
>> Allowing user-provided names may shadow existing variables without compiler warnings.
>> The complexity and freedom of let and var placement can introduce bugs in edge cases.
>> -- E
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> 

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