[swift-evolution] Auto-generate op==?
Developer
devteam.codafi at gmail.com
Sat Feb 13 15:37:55 CST 2016
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> 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> 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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