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

[Goffredo Marocchi]

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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