[swift-evolution] [Oversight] Reference types allow mutating methods through generics

[Dave Abrahams]

on Thu May 05 2016, Matthew Johnson <matthew-AT-anandabits.com> wrote:

> Sent from my iPad
>
>> On May 5, 2016, at 10:59 AM, Dave Abrahams <dabrahams at apple.com> wrote:
>> 
>> 
>> on Wed May 04 2016, Matthew Johnson <matthew-AT-anandabits.com> wrote:
>> 
>>>> On May 4, 2016, at 4:16 PM, David Sweeris <davesweeris at mac.com> wrote:
>>>> 
>>>> Having given it some more thought... Does "PureReference" make
>>>> sense? What would it mean? At some point a reference has to, you
>>>> know, actually refer to a concrete value. Otherwise it's just
>>>> turtles all the way down.
>>> 
>>> In my thinking PureReference (or ImmutableObject) has semantics
>>> indicating that the type is a value-semantic reference type.  I think
>>> this could be quite useful in some cases.
>> 
>> Like what? To a first approximation, the only thing I can see this being
>> useful for is Objective-C interop.  Aside from being an element of an
>> NSArray, there's nothing a an immutable class can do that a struct
>> can't.
>
> Objective-C / cocoa interop is important enough to matter IMO.

Sure.  I don't see why we should have an ImmutableObject protocol when
we can just compose “Immutable” with “AnyObject.”

>
>
>> 
>>> 
>>> 
>>>> 
>>>> Sent from my iPhone
>>>> 
>>>>> On May 4, 2016, at 13:32, Matthew Johnson <matthew at anandabits.com> wrote:
>>>>> 
>>>>> 
>>>>>> On May 4, 2016, at 1:21 PM, David Sweeris via swift-evolution <swift-evolution at swift.org> wrote:
>>>>>> 
>>>>>> 
>>>>>>> On May 4, 2016, at 11:12, Joe Groff via swift-evolution <swift-evolution at swift.org> wrote:
>>>>>>> 
>>>>>>> I can see value in there being some kind of PureValue protocol,
>>>>>>> for types that represent fully self-contained values, but
>>>>>>> conforming to that protocol requires a bit more thought than just
>>>>>>> being a struct or enum, since there are structs that have
>>>>>>> reference semantics (such as UnsafePointer), and there are hybrid
>>>>>>> value types that contain references to data that isn't part of
>>>>>>> the value (an Array<Class>, for instance).
>>>>>>> 
>>>>>>> -Joe
>>>>>> 
>>>>>> +1
>>>>>> 
>>>>>> I'd think that both "PureValue" and "PureReference" would be
>>>>>> useful. Isn't it the mixed types that make for tricky mutation
>>>>>> rules & serialization?
>>>>> 
>>>>> I also like Joe’s idea.  It fits with the direction in Swift of attaching semantics, not just syntax, to protocols.
>>>>> 
>>>>> I was thinking of something pretty similar to your PureReference
>>>>> idea, but slightly different.  Pure / immutable references have
>>>>> value semantics.  With that in mind I was thinking of an
>>>>> ImmutableObject protocol which would inherit from both AnyObject
>>>>> and PureValue.
>>>>> 
>>>>> 
>>>>>> _______________________________________________
>>>>>> swift-evolution mailing list
>>>>>> swift-evolution at swift.org
>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>> 
>> -- 
>> Dave

-- 
Dave