[swift-evolution] [Proposal] Union Type

[Cao Jiannan]

But in the union type design, String == String | String, this is always true

> I already answered that question:
> 
> For example:
> 
> typealias ABC = A | B | C
> 
> typealias ABCD = ABC | D
> 
> we just use an existed type ABC to construct ABCD
> 
> But how about generic wrap?
> 
> Bikeshedding:
> 
> // we generate the boundary with `A | B` or directly OneOf<A, B> enum OneOf<...T> { ...case $#(T) // Bikeshedding variadic enum casses: // we might need an index to set the value? init(index: Int, value: T) { self = .$index(value) } } /// Usage: /// A | B | C == OneOf<A, B, C> func |<T, U>(_: T.Type, _: U.Type) -> OneOf<T, U>.Type { // I also use the proposal to remove `.self` magic here return OneOf<T, U> } // Here is how to merge OneOf into a single dimension func |<...T, U>(_: OneOf<...T>.Type, _: U.Type) -> OneOf<...T, U>.Type { // Copy and merge types into the new `OneOf` type return OneOf<...T, U> } func |<T, ...U>(_: T.Type, _: OneOf<...U>.Type) -> OneOf<T, ...U>.Type { // Copy and merge types into the new `OneOf` type return OneOf<T, ...U> } func |<...T, ...U>(_: OneOf<...T>.Type, _: OneOf<...U>.Type) -> OneOf<...T, ...U>.Type { // Copy and merge types into the new `OneOf` type return OneOf<...T, ...U> }
> Your example will become:
> 
> typealias ABC = A | B | C // or OneOf<A, B, C> typealias ABCD = ABC | D // merging lhs OneOf with D to OneOf<A, B, C, D>
> Mission accomplished.
> 
> Again this is not a true union type because String | String != String
> 
> You’d get a OneOf enum with both first and second case as A. You still can distinguish them by the indexed label.
> 
> let test = OneOf<A, A>.init(index: 0, value: A()) switch test { case .$1(let value) // do something case .$2(let value) // do something }
Again this is all bikeshedding of variadic generics and variadic enums!

> 在 2016年7月1日，21:35，Cao Jiannan <frogcjn at 163.com> 写道：
> 
> what if OneOf<A, A>?
> 
> duplicate variable compile warning?
> 
>> 在 2016年7月1日，20:59，Adrian Z. <notifications at github.com <mailto:notifications at github.com>> 写道：
>> 
>> Just one simple thing to add:
>> 
>> If ...T equals 10 then <...T, U> = 10 + 1 = 11 types
>> If ...U equals 17 then <T, ...U> = 1 + 17 = 18 types
>> If ...T equals 20 and ...Uequals 22 then <...T, ...U> = 20 + 22 = 42 types
>> —
>> You are receiving this because you were mentioned.
>> Reply to this email directly, view it on GitHub <https://github.com/apple/swift-evolution/pull/404#issuecomment-229940122>, or mute the thread <https://github.com/notifications/unsubscribe/ABsfmhH9yasaWK8vAs17DGXWHV54QuCkks5qRQ9KgaJpZM4JC7-2>.
>> 
>>> 
>> 
>>> 在 2016年7月1日，21:33，Cao Jiannan <frogcjn at 163.com <mailto:frogcjn at 163.com>> 写道：
>>> 
>>> I can't compile your code. I'm really not sure your code will pass the complex generic check 🙃
>>> 
>>> Union version more complex or generic version?
>>> I think union version is more normal.
>>>> For example:
>>>> 
>>>> typealias ABC = A | B | C
>>>> 
>>>> typealias ABCD = ABC | D
>>>> 
>>>> we just use an existed type ABC to construct ABCD
>>>> 
>>>> But how about generic wrap?
>>>> 
>>>> Bikeshedding:
>>>> 
>>>> // we generate the boundary with `A | B` or directly OneOf<A, B>
>>>> enum OneOf<...T> {
>>>> 
>>>>     ...case $#(T)
>>>> 
>>>>     // Bikeshedding variadic enum casses:
>>>>     // we might need an index to set the value?
>>>>     init(index: Int, value: T) {
>>>> 
>>>>         self = .$index(value)
>>>>     }
>>>> }
>>>> 
>>>> /// Usage:
>>>> /// A | B | C == OneOf<A, B, C>
>>>> func |<T, U>(_: T.Type, _: U.Type) -> OneOf<T, U>.Type {
>>>> 
>>>>     // I believe the usage of `type` like this was prposed by Joe Groff
>>>>     // I also use the proposal to remove `.self` magic here
>>>>     return OneOf<T, U>
>>>> }
>>>> 
>>>> // Here is how to merge OneOf into a single dimension
>>>> func |<...T, U>(_: OneOf<...T>.Type, _: U.Type) -> OneOf<...T, U>.Type {
>>>> 
>>>>     // Copy and merge types into the new `OneOf` type
>>>>     return OneOf<...T, U>
>>>> }
>>>> 
>>>> func |<T, ...U>(_: T.Type, _: OneOf<...U>.Type) -> OneOf<T, ...U>.Type {
>>>> 
>>>>     // Copy and merge types into the new `OneOf` type
>>>>     return OneOf<T, ...U>
>>>> }
>>>> 
>>>> func |<...T, ...U>(_: OneOf<...T>.Type, _: OneOf<...U>.Type) -> OneOf<...T, ...U>.Type {
>>>> 
>>>>     // Copy and merge types into the new `OneOf` type
>>>>     return OneOf<...T, ...U>
>>>> }
>>>> Your example will become:
>>>> 
>>>> typealias ABC = A | B | C // or OneOf<A, B, C>
>>>> typealias ABCD = ABC | D // merging lhs OneOf with D to OneOf<A, B, C, D>
>>>> Mission accomplished.
>>>> 
>>>> 
>>>>> 在 2016年7月1日，17:06，Cao Jiannan <frogcjn at 163.com <mailto:frogcjn at 163.com>> 写道：
>>>>> 
>>>>> https://github.com/frogcjn/swift-evolution/blob/master/proposals/xxxx-union-type.md <https://github.com/frogcjn/swift-evolution/blob/master/proposals/xxxx-union-type.md>
>>>>> 
>>>>> Hi,
>>>>> 
>>>>> I'm now officially proposal the union type feature for Swift. Please see:
>>>>> 
>>>>> 
>>>>> https://github.com/apple/swift/commit/eb7311de065df7ea332cdde8782cb44f9f4a5121 <https://github.com/apple/swift/commit/eb7311de065df7ea332cdde8782cb44f9f4a5121>
>>>>> Introduction
>>>>> 
>>>>> Add union type grammar, represents the type which is one of other types.
>>>>> 
>>>>> var stringOrURL: String | URL = "https://www.apple.com <https://www.apple.com/>"
>>>>> 
>>>>> 
>>>>> I would be thankful if someone support this idea and give some advice. Thanks!
>>>>> 
>>>>> 
>>>>> --
>>>>> Jiannan
>>>>> 
>>>>> 
>>>> 
>> 

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