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

[Goffredo Marocchi]

Sent from my iPhone

> On 31 Jul 2016, at 21:19, Sean Alling via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I disagree with this suggestion.  Both a protocol conformance & class inheritance define behavior conformance.  If anything the protocol is more explicitly shown because the required properties and methods are conformed to within its declaration.

Especially in a language without abstract classes, inheritance and protocol conformance have a quite important distinction: protocols are about decoupling concrete implementation from behaviour which is not what inheritance allows or promises.

> 
> We used to define protocol conformance like so:  <myProtocol>
> This was removed to make protocol-oriented programming a bit more powerful I’d suspect.  Also, it reads much easier in the current syntax.  
> 
> If we were to change it, I would suggest a keyword ‘conform’ because your suggested operators don’t make it explicit what behavior is being defined. Whereas, the current syntax behavior is simple and easily understood.
> 
> Sean
> 
> 
> 
> 
>> 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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