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

[Patrick Gili]

I've been playing with the concept in Haskell, and I like the concept. However, I don't like the proposed syntax, as it is not consistent the rest of the language. Maybe something like

struct Person : deriving Equatable {
    let age: Int
    let name: String
}

or 

struct Person : @deriving Equatable {
    let age: Int
    let name: String
}

-Patrick

> 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 <mailto: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 <mailto: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 <mailto: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,
>>>> 
>>>> _______________________________________________
>>>> swift-evolution mailing list
>>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>>> 
>>> _______________________________________________
>>> swift-evolution mailing list
>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>> 
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160213/6c8a21b4/attachment.html>