[swift-evolution] [Draft] Mixins

[Howard Lovatt]

I would think that:

Example: A -> (B, C) -> D
B.init calls A.super.init(1)
C.init calls A.super.init(2)
D.init calls B.super.init() and C.super.init()

is an error because there is one A and you have inited it twice. Just like
calling super twice is an error currently.

On Wednesday, 27 April 2016, Антон Жилин <swift-evolution at swift.org> wrote:

> Yes, this is my proposal, and of course, I'm interested :)
>
> I haven't read into the mentioned papers, but symmetric sum, asymmetric
> sum, alias, exclusion and derived operations form a solid basis for
> conflict resolution.
> Mixins don't have all that tools and try to solve conflicts by being less
> strict at composition.
> I agree that Swift, as a compiled language, would benefit from the former
> more.
>
> In traits, I like how requirements and definitions are separated using
> requirement of protocol conformance.
> It follows Uniform Access Principle: noone can require conformance to a
> trait.
> Are there other benefits?
>
> I believe there are situations where non-privateness of fields would help,
> see my two examples.
> This can be overridden by adding a "proxy" computed property. But why is
> privateness needed?
>
> Do traits have initializers? How do they work in diamond pattern?
>
> Example: A -> (B, C) -> D
> B.init calls A.super.init(1)
> C.init calls A.super.init(2)
> D.init calls B.super.init() and C.super.init()
>
> Traits are flattened by default. Does it mean that A will be initialized
> twice? in what state will A be?
>
> - Anton
>
> 2016-04-27 2:50 GMT+03:00 Niall Young <niall at iinet.net.au
> <javascript:_e(%7B%7D,'cvml','niall at iinet.net.au');>>:
>
>> On Fri, 22 Apr 2016, Антон Жилин wrote:
>>
>> This feature has been previously discussed. Search for Mixins on
>>> swift-evolution archives.
>>>
>>> I believe it would help to read previous version of the proposal:
>>> https://github.com/Anton3/swift-evolution/blob/mixins/proposals/NNNN-mixins.md
>>>
>>
>> Cheers, already read through the thread - I'm more focused on
>> implementing Traits, which I think is very similar but slightly different
>> to what's been described in the thread to date.
>>
>> Is this your proposal?  I'd love to give you some feedback, throw ideas
>> back and forth if you're interested?  If we can evolve the concept and
>> implementation by Swift 4 that gives me enough time to brush up on C++ and
>> start delving into Swift internals to see how best it could be done.
>>
>> Cheers,
>>
>> --
>> Niall Young
>> niall at iinet.net.au <javascript:_e(%7B%7D,'cvml','niall at iinet.net.au');>
>
>
>

-- 
-- Howard.
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