[swift-evolution] Protocols and var { get }

[Howard Lovatt]

If we assume that Swift was changed to be like Scala then:

    protocol Stored {
        let x = 42
    }

Would be equivalent to:

    protocol Stored {
        var x: Int { get }
        static func initX() -> Int
    }

    extension Stored {
        static func initX() -> Int { return 42 }
    }

If you then implemented the protocol:

    struct S: Stored {
        var x = 69 // Could be `let` instead of `var`
    }

Would be equivalent to:

    struct S: Stored {
        var x = S.initX()
        static func initX() -> Int { return 69 }
    }

Therefore it is possible to unify the two concepts.

On Saturday, 30 January 2016, <davesweeris at mac.com> wrote:

> Not really… There’s a pretty big difference between “no setter” and
> “const". Plus, since we’re talking about protocols, “var … {get}” doesn’t
> even mean “no setter”, it means “no setter *required*”. A regular var
> property (which is obviously not constant) can satisfy a {get} requirement.
>
> - Dave Sweeris (Non-Canonical Dave)
>
> On Jan 29, 2016, at 22:49, Howard Lovatt via swift-evolution <
> swift-evolution at swift.org
> <javascript:_e(%7B%7D,'cvml','swift-evolution at swift.org');>> wrote:
>
> Scala uses their equivalent of let ... instead of var ... { get }. In
> Scala let ... Always means var ... { get }. Not a problem in Scala only
> having one concept. I think it is a possibility for Swift.
>
> On Saturday, 30 January 2016, Brent Royal-Gordon via swift-evolution <
> swift-evolution at swift.org
> <javascript:_e(%7B%7D,'cvml','swift-evolution at swift.org');>> wrote:
>
>> > So what about protocols requiring ‘var … { get }’ syntax for read only
>> properties? Is there some sort of underlying reason for this confusing
>> syntax instead of ‘let …’? Now that Swift allows deferred initialization of
>> lets does this requirement make sense?
>>
>> `let` doesn't mean "no setter", it means "constant". For instance, you
>> can't make a `weak let`, because the `weak` implies the variable can be
>> nilled. There's no way to require a constant in a protocol, but if there
>> were one, that's what `let ...` would mean.
>>
>> --
>> Brent Royal-Gordon
>> Architechies
>>
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>>
>
>
> --
>   -- Howard.
>
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>

-- 
  -- Howard.
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