[swift-evolution] isEqual to replace == Equatable Requirement

[David Hart]

Well in that case I find even more confusing that to implement equality you have to define a function which is different from the operator.

> On 08 Dec 2015, at 18:43, Richard Fox <fox.ios.dev at gmail.com> wrote:
> 
> I dont see how this makes it less readable, are you taking into consideration that you still use == everywhere for comparison, after defining with isEqual? As this method would be defined in the stdlib.
>>> public func == <T : Equatable>(lhs: T, rhs: T) -> Bool 
> 
>> On Tue, Dec 8, 2015 at 5:36 AM David Hart <david at hartbit.com> wrote:
>> Your proposition makes comparison code much less readable only for a small benefit at the point of definition. I'd vote against.
>> 
>>> On 08 Dec 2015, at 11:06, Nicky Gerritsen via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> Although I like the idea, I think it should be more general, as this same reasoning also holds for other operators.
>>> Wouldn't it be better to allow to define operators within a type? So that we can just implement == in the type?
>>> 
>>> I do not know how hard it is to implement it or if this is even possible. Probably it is hard, because otherwise it would already have been done?
>>> Regards,
>>> 
>>> Nicky
>>>> On 12/08/2015 11:01 AM, Richard Fox via swift-evolution wrote:
>>>> Hi all,
>>>> I would like to propose changing the Equatable protocol to use isEqual(to:Self) -> Bool, defined inside of a type to replace the currently used operator == function, which is defined outside of the type.
>>>> 
>>>> Reasoning:
>>>> 
>>>> Having the conforming function defined inside of the type is more intuitive, since in general functions required for conformance are defined within the type. It feels like an unnecesary detail for learners of Swift to have to stumble through.
>>>> The implementation for this would look something like this:
>>>> 
>>>>      public protocol Equatable{
>>>>        ....
>>>> 
>>>>        /// Shortcut for defining `==` function inside type definition.
>>>>        @warn_unused_result
>>>>        func isEqual(to:Self) -> Bool
>>>>      }
>>>> 
>>>>      @warn_unused_result
>>>>      public func == <T : Equatable>(lhs: T, rhs: T) -> Bool {
>>>>          return lhs.isEqual(rhs)
>>>>      }
>>>> Impact on Existing Code:
>>>> 
>>>> This implementation would break existing code, but could be fixed with a default protocol extension such as:
>>>> 
>>>>      /// Default `isEqual` function to satisfy other types only definiting
>>>>      /// `==` for equality.
>>>>      public extension Equatable{
>>>>          func isEqual(to:Self) -> Bool{
>>>>              return self == to
>>>>          }
>>>>      }  
>>>> Not adding the default function for isEqual makes more sense to me though, since it would remove any strict requirement for Equatable conformance and leave no warning for the loop you would create by implementing neither isEqual nor ==.
>>>> 
>>>> Regards,
>>>> Rich Fox
>>>> 
>>>>  
>>>> 
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>>> 
>>> 
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