[swift-evolution] [Pitch] separate syntax of class inheritance and protocol conformance

[Xiaodi Wu]

On Fri, Jul 22, 2016 at 1:04 PM, Goffredo Marocchi <panajev at gmail.com>
wrote:

> This adds information without being a burden while the current approach
> mixes and matches in a workable but less consistent way.
>

It adds no *useful* information.

Adopting a protocol is not the same as subclass for, why should it look the
> same syntax wise?
>

As Daniel has pointed out, `class A : P { ... }` establishes a relationship
such that `A is P`, regardless of whether P is a protocol or base class.

Sent from my iPhone
>
> On 22 Jul 2016, at 19:00, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>
> On Fri, Jul 22, 2016 at 12:42 PM, Leonardo Pessoa via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> It would still cause confusion if you were only to conform to a single
>> protocol (P in "class A : P" is a class or a protocol?). This can be
>> solved in code but I don't think it is necessary.
>>
>
> The point made earlier is salient: if you know what P is, no clarification
> is necessary; on the other hand, if you don't know anything else about P,
> knowing whether P is a class or protocol is essentially useless even if
> you're a reader. What could you possibly do with this information?
>
> L
>>
>>
>> On 22 July 2016 at 14:08, Goffredo Marocchi via swift-evolution
>> <swift-evolution at swift.org> wrote:
>> > I think that the current approach marks a regression in declarative
>> > expressiveness as the notion of extending a class over implementing a
>> > protocol is blurred while the concepts are IMHO not the same (the
>> latter is
>> > about behaviour conformance not a is a relationship):
>> >
>> > Class/struct B : Class/struct A <Protocol1 & Protocol2>
>> >
>> >
>> > would be a clear and concise way to express it that would not be
>> confused
>> > even at a quick glance.
>> >
>> > Sent from my iPhone
>> >
>> > On 22 Jul 2016, at 14:47, Charlie Monroe via swift-evolution
>> > <swift-evolution at swift.org> wrote:
>> >
>> > I agree that this is an issue. Mostly nowadays when more and more
>> classes in
>> > Swift do not have a superclass - it simply looks weird:
>> >
>> > class MyClass: DataSource
>> >
>> > One doesn't know whether "DataSource" is a class, protocol, etc.
>> > Nevertheless, I do not feel that :: is the answer. I really liked, how
>> ObjC
>> > did it (which isn't possible with the generics now - is it?), but what
>> about
>> > something like this?
>> >
>> > class BaseClass [SomeDelegate, OtherDelegate, ProtocolX]
>> > class MyClass: BaseClass [SomeDelegate, OtherDelegate, ProtocolX]
>> > extension MyClass [OtherProtocol]
>> >
>> >
>> > On Jul 22, 2016, at 3:14 PM, Vladimir.S via swift-evolution
>> > <swift-evolution at swift.org> wrote:
>> >
>> >
>> > I remember that this was discussed, but can't find any decision
>> regarding
>> > this.. So, as a last chance, don't we want in Swift 3.0, as big source
>> > breaking change, separate class inheritance and protocol conformance in
>> > syntax?
>> >
>> >
>> > Sorry if there was a decision about this suggestions. Please let know in
>> > this case.
>> >
>> >
>> > I.e. when I see the following I can't understand if the class inherits
>> from
>> > base class and conforms to protocols or just conforms to two protocols:
>> >
>> >
>> > class MyClass : First, Second, Third {
>> >
>> > }
>> >
>> >
>> > We don't have a rule to name protocols with 'Protocol'/other
>> suffix/prefix,
>> > or classes with 'T'/'C' prefix or something like this, so I believe to
>> > improve the clarity of code we should separate in syntax inheritance and
>> > conformance.
>> >
>> >
>> > As I understand we should discuss changes in these areas:
>> >
>> >
>> > 1. class inheritance :
>> >
>> > class Child: BaseClass
>> >
>> >
>> > 2. class conformance :
>> >
>> > class Child: SomeProtocol1, SomeProtocol2
>> >
>> >
>> > 3. class inheritance + conformance :
>> >
>> > class Child: BaseClass, SomeProtocol1, SomeProtocol2
>> >
>> >
>> > 4. protocol conformance for structs:
>> >
>> > struct Struct: SomeProtocol1, SomeProtocol2
>> >
>> >
>> > 5. protocol inheritance:
>> >
>> > protocol Child: BaseProtocol1, BaseProtocol2
>> >
>> >
>> >
>> > My suggestions:
>> >
>> >
>> > I) separate inheritance with double colon :
>> >
>> >
>> > 1. class inheritance :
>> >
>> > class Child:: BaseClass
>> >
>> >
>> > 2. class conformance :
>> >
>> > class Child: SomeProtocol1, SomeProtocol2
>> >
>> >
>> > 3. class inheritance + conformance :
>> >
>> > class Child:: BaseClass : SomeProtocol1, SomeProtocol2
>> >
>> >
>> > 4. protocol conformance for structs:
>> >
>> > struct Struct: SomeProtocol1, SomeProtocol2
>> >
>> >
>> > 5. protocol inheritance:
>> >
>> > protocol Child:: BaseProtocol1, BaseProtocol2
>> >
>> >
>> >
>> > II) in class definition use parenthesis to separate inheritance and
>> > conformance :
>> >
>> >
>> > 1. class inheritance :
>> >
>> > class Child: BaseClass
>> >
>> >
>> > 2. class conformance :
>> >
>> > class Child: (SomeProtocol1, SomeProtocol2)
>> >
>> >
>> > 3. class inheritance + conformance :
>> >
>> > class Child: BaseClass (SomeProtocol1, SomeProtocol2)
>> >
>> >
>> > 4. protocol conformance for structs:
>> >
>> > struct Struct: SomeProtocol1, SomeProtocol2
>> >
>> > or
>> >
>> > struct Struct: (SomeProtocol1, SomeProtocol2)
>> >
>> > should be discussed
>> >
>> >
>> > 5. protocol inheritance:
>> >
>> > protocol Child: BaseProtocol1, BaseProtocol2
>> >
>> >
>> >
>> > III) special word like 'conforms'
>> >
>> >
>> > 1. class inheritance :
>> >
>> > class Child: BaseClass
>> >
>> >
>> > 2. class conformance :
>> >
>> > class Child: conforms SomeProtocol1, SomeProtocol2
>> >
>> > or
>> >
>> > class Child conforms SomeProtocol1, SomeProtocol2
>> >
>> >
>> > 3. class inheritance + conformance :
>> >
>> > class Child: BaseClass conforms SomeProtocol1, SomeProtocol2
>> >
>> >
>> > 4. protocol conformance for structs:
>> >
>> > struct Struct: conforms SomeProtocol1, SomeProtocol2
>> >
>> > or
>> >
>> > struct Struct conforms SomeProtocol1, SomeProtocol2
>> >
>> >
>> > 5. protocol inheritance:
>> >
>> > protocol Child: BaseProtocol1, BaseProtocol2
>> >
>> >
>> >
>> > Thoughts?
>> >
>> > _______________________________________________
>> >
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>> >
>> > swift-evolution at swift.org
>> >
>> > https://lists.swift.org/mailman/listinfo/swift-evolution
>> >
>> >
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>> >
>> >
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