[swift-evolution] [SE-0011] Re-considering the replacement keyword for "typealias"

[James Campbell]

If we made class, structs, protocols and functions use the same generics
syntax then I think it would make it more consistent rather than arguing
about which keyword to use. I am for-ever being tripped up by lack of
generics in the language.

class Array<T>
{
func first() -> T?
}

struct Node<Value>
{
var value: Value
}

Array<Int>()
Node<Int>()

or

func makeACell<T>() -> T
{
}

makeACell<MyCell>()

or

protocol Collection<Item>
{
func first() -> Item?
}

class IntBag : Collection<Int> //We bind protocol "associated type" using
generic syntax when subclassing. In this case we are saying Item should be
type Int
{
}

class Array<Item>: Collection<Item> //We bind protocol "associated type"
using generic syntax when subclassing. In this case we are saying Item
should be the same type as the generic type for Array
{
}

IntBag()
Array<Int>()


On Wed, Dec 23, 2015 at 10:58 PM, James Campbell <james at supmenow.com> wrote:

> They are placeholders because in the protocol:
>
> prtocotol Collection
> {
>   placeholder Item
>
>   func first() -> Item?
>  {
>  }
> }
>
> Item is a placeholder for a concrete type, at this moment this is a
> concept "A collection should return an item of a type" but we don't know
> what that type is as its a plaeholder for a type.
>
> therefore in:
>
> class IntCollection: Collection
> {
>    placeholder Item = Int
> }
>
> We are saying that the placeholder should now become a concrete type. In
> my eyes associated types are nothing more than generics for protocols which
> in turn could be argued is some kind of placeholder.
>
> Associated type means nothing to me, associated to what ? A type could be
> associated to many things like a variable, or a generic or whatever. A
> placeholder to mean does what it says on the tin. If we moved to protocols
> using a syntax closer to generics for classes then I think it would be
> simpilar to grasp for beginners .
>
> On Wed, Dec 23, 2015 at 9:35 PM, Jordan Rose <jordan_rose at apple.com>
> wrote:
>
>> James or Erica (or someone else), can you explain what makes these types
>> "placeholders"? I don't think of the other requirements in a protocol as
>> "placeholder properties" or "placeholder methods".
>>
>> My explanation of these things is "When a particular type X conforms to a
>> protocol, you can ask about the types that X uses to implement the
>> requirements of the protocol". I guess we could call them "related types"
>> instead of "associated types", but that doesn't seem significantly
>> different.
>>
>> Jordan
>>
>>
>> > On Dec 23, 2015, at 12:42, James Campbell via swift-evolution <
>> swift-evolution at swift.org> wrote:
>> >
>> > The thing is associated type means nothing to me, it's too technical.
>> Placeholder type I think would be better even if it's only what we called
>> it in the documentation
>> >
>> > Sent from my iPhone
>>
>>
>
>
> --
>  Wizard
> james at supmenow.com
> +44 7523 279 698
>



-- 
 Wizard
james at supmenow.com
+44 7523 279 698
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