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

[Ian Partridge]

Now that SE-0095 is accepted, I think it would be a good idea to use
the infix & operator for specifying protocol conformance as well.

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

Thanks,
Ian

On 22 July 2016 at 14:14, 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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-- 
Ian Partridge