Lets sum things up before I try to write a draft proposal for this feature
`type<>` aka `all<>`.
Is this feature out of scope for Swift 3?
From my point of view it’s definitely not.
Is the name `type<>` really that bad for the compiler?
Here I’m not sure, because that is out of my experience. From a readers
perspective it’s more clear than `all<>`, I would say, even though this is a
perfect explanation why it should be called `all<>`:
I also see Thorsten (and in the past Brent's?) argument for calling it "all" or
"All", because it's enforcing multiple constraints.
Do we miss any rules here?
`type<>` can contain only one value-type or reference-type and n protocols
the value-type or reference-type should always be the first element between
angle brackets
`type<>` should always contain at least 2 types (one value-type or a
reference-type and at least one protocol)
reference-types do represent a possible super/base type/class
nesting `type<>` is not allowed, however `type<>` can contain `protocol<>`
protocols conformance of `type<>` is tested with the actual type `type<>` not
with the first element of `type<>` (hard to describe this one, does this makes
sense to you?)
Does this proposal need more than the base `type<>`?
Maybe, but I think we should start with `type<>` before we will introduce a
type operator for this.
Did I missed anything out here?
PS: Feel free to help me with my English, because it’s not so well.
--
Adrian Zubarev
Sent with Airmail
Am 13. Mai 2016 bei 16:21:41, Tony Allevato (allev...@google.com) schrieb:
I think there would be a certain elegance to allowing Boolean type expressions
wherever types are currently allowed, so `A & B` being a replacement for
`protocol<A, B>` might look nice, and then extend that to allow concrete types
as well. Then, if Swift ever decided to support union types, the `|` operator
naturally fits there.
One concern though would be whether parsing would get more complicated with
deeply composed expressions. If we only supported `&`, there's no real nesting
going on. But if we wanted to be forward thinking and leave the door open for
`|`, we might need to support things like `(String | Int) & SomeProtocol`, and
I'm not enough of a parser expert to know whether that would really complicate
things (e.g., could the compiler decide easily enough that those parentheses
are part of a type expression and not a function type?).
`all<A, B>` would be a nice compromise in that case, and leave the door open
for `any<A, B>` in the future. So I'd be supportive of either option.
On Thu, May 12, 2016 at 1:30 PM Jordan Rose via swift-evolution
<swift-evolution@swift.org> wrote:
We've been over this a few times before on the list. I personally like naming
this thing "Any<…>" in the same vein as "AnyObject", "AnyClass", and
"AnySequence". I also see Thorsten (and in the past Brent's?) argument for
calling it "all" or "All", because it's enforcing multiple constraints.
I will say that "type" is unlikely to see much traction simply because it is an
incredibly common name for both properties and locals. We went through that
exercise when trying to name both "static" and "dynamicType" and decided that
it would be too confusing, even if we could make the parsing work.
The feature itself has definitely been shown to be useful when working with the
Cocoa frameworks, if not in general. I don't see it on JIRA yet but we have it
internally tracked in Radar as rdar://problem/15873071.
Jordan
On May 12, 2016, at 13:08, Adrian Zubarev via swift-evolution
<swift-evolution@swift.org> wrote:
I don’t get the part how `all<>` should allow `any<>`. Could you explain that a
little bit in detail (I’m not familiar with Ceylon)?
>From my point of view `any<>` is something different that I pitched here.
>`any<>` could be proposed in its own thread, because it is way different than
>`type<>`. Or can we refine the rules of `type<>` to get to `any<>`?
Here is a little example where `any<>` gets strange:
func foo(value: any<String, Int>) -> any<String, Int> {
// how would one use value here?
// what about its properties
// what will foo return and how to use the result
}
One benefit of `any<>` is the replacement of overloading, at least for the type
part of the function.
I’d like to propose `type<>` as the base extension to the language in that
direction, before we’ll move forward with more complex scenarios (just like
Chris did with generic typealias).
This function is clear that it only will work if you provide a subclass of an
UIView which conforms to SomeProtocol (nice addition for library design).
func foo(value: type<UIView, SomeProtocol>) -> type<UIView, SomeProtocol> {
// use it as a UIView and SomeProtocol at the same type
return value // return type works great
}
We can split the value just fine:
let mergedValue = foo(SomeViewThatWorks)
let view: UIView = mergedValue
let protocolValue: SomeProtocol = mergedValue
And merge it back together:
guard let newMergedValue = view as? type<UIView, SomeProtocol> else { /* do
something */ }
`all<>` could be seen as an alternative name for `type<>`, but to me its not
clear what `all<>` can do, whereas `type<>` is almost like `protocol<>`.
--
Adrian Zubarev
Sent with Airmail
Am 12. Mai 2016 bei 21:40:24, Thorsten Seitz (tseit...@icloud.com) schrieb:
Ceylon uses „&" for intersection types, i.e.
SomeRealClass & SomeProtocol
and the bar („|“) for union types, i.e.
String | Int
That has proven to be very lightweight and readable in Ceylon where it is
heavily used to good effect.
I agree with you that
type<SomeRealClass, SomeProtocol>
is much nicer than protocol<> for intersection types but to keep the door open
for union types, I would prefer
all<SomeRealClass, SomeProtocol>
This would allow
any<String, Int>
to be used for union types.
-Thorsten
Am 12.05.2016 um 16:09 schrieb Adrian Zubarev via swift-evolution
<swift-evolution@swift.org>:
protocol<SomeRealClass, SomeProtocol>
protocol<SomeRealStruct, SomeProtocol>
This feels really odd to me.
`type<SomeRealClass, SomeProtocol>` is more clear I’d say.
I think this would be a good addition to the type system and allow us to build
more complex and type save code.
But still I’d love to discuss if there might be any disadvantages to this
feature.
--
Adrian Zubarev
Sent with Airmail
Am 12. Mai 2016 bei 15:11:00, Vladimir.S (sva...@gmail.com) schrieb:
protocol<>
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