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

[Leonardo Pessoa]

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.

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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