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

[Nicky Gerritsen]

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.
>
>
>       <https://gist.github.com/Nadohs/308603afa65cbbfba07c#reasoning>Reasoning:
>
>  1. 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) } |
>
>
>       <https://gist.github.com/Nadohs/308603afa65cbbfba07c#impact-on-existing-code>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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