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

[Xiaodi Wu]

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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> >
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> >
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> >
> >
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