[swift-evolution] Auto-generate op==?

[danielt1263 at gmail.com]

Yes, that's exactly what I am suggesting. Maybe even do the same for Hashable. (And any other protocol where there is an obvious implementation...)

As for syntax, I don't much care. A "deriving" keyword could be added, or maybe if you mark the type as Equatable and don't provide an implantation, it would auto-generate one for you, or error out.

I personally feel that most value types should be equatable, but I tend not to do it purely because of all the boilerplate required. This sort of mechanism would help tremendously. 

I don't see any reason to limit such an idea to just value types, but that is where it's most  needed IMHO.

Based on an earlier comment, this type of feature would probably have to wait until 3.0, but I wanted to put the idea out there.


Sent from my iPad

> On Feb 13, 2016, at 12:38 PM, Donald Pinckney <djpinckney at ucdavis.edu> wrote:
> 
> To make sure I understand correctly, what you are discussing is having == be auto generated in some way for types. The automatic implementation of == would be a member wise logical and operation:
> 
> struct Person {
>    let age: Int
>    let name: String
> } deriving Equatable
> 
> Would also generate:
> func ==(left: Person, right: Person) -> Bool {
>    return left.age == right.age && left.name == right.name;
> }
> 
> The compiler would only do this if all data members implement (or derive) the Equatable protocol, and probably error otherwise.
> 
> That's my interpretation.  If I misunderstood, please correct me.  
> 
> As it stands, I think something like this is a fabulous idea, as I have recently found myself writing lots of member wise equality checks.
> 
> Donald Pinckney
> 
> Sent from my iPhone
> 
>> On Feb 13, 2016, at 9:12 AM, Donnacha Oisín Kidney via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> In Haskell, when you declare a datatype, you can follow it with a “deriving” clause, and it will derive several typeclasses (which are Haskell’s equivalent to protocols):
>> 
>> data Person = Person { name :: String, age :: Int } deriving Eq
>> 
>> In Swift, I’d imaging the equivalent would be something like:
>> 
>> struct Person {
>>   let name: String
>>   let age: Int
>> } deriving Equatable
>> 
>>> On 13 Feb 2016, at 17:04, Patrick Gili via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> Not having a lot of experience with Haskell, can you provide an example, so that we can better understand what you're proposing?
>>> 
>>> Cheers,
>>> -Patrick
>>> 
>>>> On Feb 12, 2016, at 3:47 PM, Daniel Tartaglia via swift-evolution <swift-evolution at swift.org> wrote:
>>>> 
>>>> In Haskell, we can mark a data block as deriving from Eq and it will auto-generate the == operator.
>>>> 
>>>> I would like to see Swift auto-generate the == operator if a struct implements Equatable. Obviously, it would only be able to do this if all the structs members implemented Equatable themselves.
>>>> 
>>>> Has this idea already been proposed? I didn’t see it at the github repo…
>>>> 
>>>> Thanks,
>>>> 
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>>> 
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