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

[Vladimir.S]

On 22.07.2016 18:13, Karl wrote:
> What about if we defined subclasses with the “subclass” keyword instead of “class”? So you knew the first parameter was always going to be a base class?
>
> That way we keep the single “:” everywhere else - where clauses, generic constraints lists, etc.

I like this idea, so when I see

subclass B: A, P1, P2 {
}

or

class B : Z {
}

it is clear when it is conformance and where it is inheritance, no need in 
any additional rule to separate class/protocol, still will work if P1&P2 
syntax will be allowed, i.e.

subclass B: A, P1&P2 {
}

Also, as we are moving in Protocol-Oriented-Programming way, IMO we should 
not somehow adds complexity to syntax of conforming value types to 
protocols. So, seems like the only place where we can change the syntax - 
is inheritance of class with double colon `class Derived::Base:Protocol` or 
with this `subclass Derived: Base, Protocol`

>
>> On 22 Jul 2016, at 15:14, 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
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>
> .
>