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

[Patrick Gili]

Agreed.

In the property behaviors review, Chris Lattner mentioned that there is a trend to use # to denote compiler synthesis. Thus, this is probably a good alternative.

Cheers,
-Patrick

> On Feb 13, 2016, at 4:37 PM, Developer <devteam.codafi at gmail.com> wrote:
> 
> I'd be in favor of forgoing the keyword addition and just prefixing compiler-derivable protocols with a # or @.  Save `deriving` for later extensions to a future generalized deriving mechanism.
> 
> ~Robert Widmann
> 
> 2016/02/13 16:29、Patrick Gili via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> のメッセージ:
> 
>> 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 <mailto: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,
>>>>>> 
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>>>>> 
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