<html><head><style>body{font-family:Helvetica,Arial;font-size:13px}</style></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">Okay I got it now, generics made my had spin. I also received no feedback on my proposal to that specific case, which I misunderstood. Thank you for clarifying that to me. That said it makes now sense to force the first requirement, which I dropped in my proposal. </div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">I’d fix that tomorrow.</div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">I’m fine with your proposal now. =) </div> <br> <div id="bloop_sign_1463606621886717952" class="bloop_sign"><div style="font-family:helvetica,arial;font-size:13px">-- <br>Adrian Zubarev<br>Sent with Airmail</div></div> <br><p class="airmail_on">Am 18. Mai 2016 bei 23:17:47, Austin Zheng (<a href="mailto:austinzheng@gmail.com">austinzheng@gmail.com</a>) schrieb:</p> <blockquote type="cite" class="clean_bq"><span><div><div></div><div>
<title></title>
<div dir="ltr">I'm not sure what your objections actually are, but
my responses are inline.<br>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Wed, May 18, 2016 at 1:57 PM, Adrian
Zubarev via swift-evolution <span dir="ltr"><<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word">
<div style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<blockquote type="cite">
<div style="word-wrap:break-word">
<blockquote type="cite">
<div>
<div style="margin:0px"><span class="">So without any initial
constraints how would one use this generic function??</span></div>
<div style="margin:0px"><span class=""><br></span></div>
<div style="margin:0px"><span class="">extension UIButton:
ProtocolA {}</span></div>
<div style="margin:0px"><span class=""><br></span></div>
<div style="margin:0px"><span class="">let button =
UIButton()</span></div>
<div style="margin:0px"><span class="">let shadowedButton:
ProtocolA = UIButton()</span></div>
<div style="margin:0px"><span class=""><br></span></div>
<div style="margin:0px"><span class="">// creates a set of a least
one element if the generic type could be inferred</span></div>
<div style="margin:0px"><span class="">func unionIfPossible<T,
U>(_ a: T, _ b: U) -> Set<Any<T, U>>? { /* merge
somehow if possible */ }</span></div>
</div>
</blockquote>
<div><span class=""><br></span></div>
<div><span class="">You would not be able to form Any<T, U>
here because T and U are generic arguments unknown. We don’t
accept those, only `class`, specific classes, and specific
protocols (and recursively, other Any).</span></div>
</div>
</blockquote>
<div style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<span class=""><br></span></div>
<div style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
Why would Any<…> does not work with the generic system here?
To me it makes no sense, I as a developer would assume I can use a
generic Type anywhere a type can be used (protocols and their
associated types are a special case).</div>
</div>
</div>
</blockquote>
<div><br></div>
<div>Because what existentials are trying to model and what generic
type parameters are trying to model are two different things. You
already cannot use arbitrary types within a Any<> existential
as the proposal stands.</div>
<div><br></div>
<div>This doesn't currently work in Swift, and it shouldn't: "func
foo<A, B>() -> protocol<A, B>". There is no useful
way to generically compose instances of two protocol types at
runtime to form an instance of a type that conforms to both
protocols, like there is a way to compose instances of two types to
form a tuple containing those types. Therefore, writing a generic
function to do this makes no sense.</div>
<div><br></div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word">
<div style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<div style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<br></div>
<div style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
I would assume that:</div>
<div style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<br></div>
<div style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
func foo<T: UIView>(value: Any<T, SomeProtocol>)</div>
<div style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<br></div>
<div style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
should be equal to (without the need of generics):</div>
<div style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<br></div>
<div style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
func foo(value: Any<UIView, SomeProtocol>)</div>
<span class=""><br></span>
<div>
<blockquote type="cite" style="font-family:Helvetica,Arial;font-size:13px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<div style="word-wrap:break-word">
<blockquote type="cite">
<div>
<div style="margin:0px"><span class=""><br>
// this should be valid because the compiler will assume
Any<UIView, ProtocolA> where T == UIView and U ==
ProtocolA</span></div>
<div style="margin:0px"><span class="">let merged_1:
Set<Any<UIView, ProtocolA>> = unionIfPossible( /*
UIView subtype */ button, /* ProtocolA */
shadowedButton) </span></div>
<div style="margin:0px"><span class=""><br></span></div>
<div style="margin:0px">
<div style="margin:0px"><span class="">// this won’t be possible
because of the restriction</span></div>
<div style="margin:0px"><span class="">let merged_2:
Set<Any<UIView, ProtocolA>> =
unionIfPossible(shadowedButton, button) </span></div>
<div style="margin:0px"><span class=""><br></span></div>
<div style="margin:0px"><span class="">Any<UIView, ProtocolA>
!= Any<ProtocolA, UIView> isn’t right. Sure it may feel right
for readability but the types should be equal.</span></div>
<div style="margin:0px"><span class=""><br></span></div>
<div style="margin:0px"><span class="">"Can be any class type that
is a UIView or a subclass of UIView, that also conforms to
ProtocolA.“ == "Type that conforms to ProtocolA and that
is a UIView or a subclass of UIView.“</span></div>
<div style="margin:0px"><span class=""><br></span></div>
<div style="margin:0px"><span class="">This is also a nesting
problem where you will be forced to choose the right place inside
the angle brackets where to add a nested
`Any<…>`.</span></div>
<div style="margin:0px"><span class=""><br></span></div>
<div style="margin:0px"><span class="">class A: ClassB, ProtocolA
{}</span></div>
<div style="margin:0px"><span class=""><br></span></div>
<div style="margin:0px"><span class="">Any<A, Any<ClassB,
ProtocolA>> == A != Any<Any<ClassB, ProtocolA>,
A> == Any<ClassB, ProtocolA, A> which should be reorder by
the compiler and inferred as A</span></div>
</div>
</div>
</blockquote>
<div><span class=""><br></span></div>
<div><span class="">`Any<Any<ClassB, ProtocolA>, A>` is
not allowed because if a class is provided it must come
first.</span></div>
<div><span class=""><br></span></div>
<div><span class="">`<span>Any<ClassB, ProtocolA, A>` is not
allowed because it contains more than one
class.</span></span></div>
</div>
</blockquote>
</div>
<p>Not true, take a look at the nested section of the proposal
again.</p>
<p>We discussed that this is valid:</p>
<pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;line-height:1.45;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;word-wrap:normal;word-break:normal;color:rgb(51,51,51)">
<span style="color:rgb(150,152,150)">// Allowed, but pointless.</span>
<span style="color:rgb(150,152,150)">// Identical to Any<ProtocolA, ProtocolB></span>
<span style="color:rgb(167,29,93)">let</span> b <span style="color:rgb(167,29,93)">:</span> <span style="color:rgb(0,134,179)">Any</span><span style="color:rgb(167,29,93)"><</span><span style="color:rgb(0,134,179)">Any</span><span style="color:rgb(167,29,93)"><</span>ProtocolA, ProtocolB<span style="color:rgb(167,29,93)">>></span>
</pre>
<div><br></div>
</div>
<div>This implies that also this would be valid:</div>
<div><br></div>
<div>Any<Any<ClassA, ProtocolA>> inferred as
Any<ClassA, ProtocolA></div>
</div>
</blockquote>
<div><br></div>
<div>Yes, this is valid.</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word">
<div><br></div>
<div>There is another example:</div>
<div><br></div>
<div>
<pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;line-height:1.45;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;word-wrap:normal;word-break:normal;color:rgb(51,51,51)">
<span style="color:rgb(150,152,150)">// Can be any type that is a UITableView conforming to ProtocolA.</span>
<span style="color:rgb(150,152,150)">// UITableView is the most specific class, and it is a subclass of the other</span>
<span style="color:rgb(150,152,150)">// two classes.</span>
<span style="color:rgb(167,29,93)">let</span> a <span style="color:rgb(167,29,93)">:</span> <span style="color:rgb(0,134,179)">Any</span><span style="color:rgb(167,29,93)"><</span>UIScrollView, <span style="color:rgb(0,134,179)">Any</span><span style="color:rgb(167,29,93)"><</span>UITableView, <span style="color:rgb(0,134,179)">Any</span><span style="color:rgb(167,29,93)"><</span>UIView, ProtocolA>>>
</pre></div>
<div><br></div>
<div>Which followed by the mentioned rule can als be:</div>
<div><br></div>
<div>Any<UIScrollView, UITableView, Any<UIView,
ProtocolA>> or</div>
<div>Any<UIScrollView, UITableView, UIView, ProtocolA></div>
<div><br></div>
<div>This would force us to allow multiple classes inside
Any<…> if there is a inheritance relationship between
them.</div>
</div>
</blockquote>
<div><br></div>
<div>Yes. As explained in the proposal, there is already a way to
handle resolving the single 'effective' class constraint. You can
only 'explicitly' declare one class constraint, but you can pull in
other class constraints from nested existentials for the sake of
making composition easier. In the end it doesn't matter, because if
the class constraints don't form a valid inheritance hierarchy the
compiler will complain, and if they do the most specific type will
be chosen.</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word">
<div><br></div>
<div>And because this is a inheritance relationship it can be
simplified to:</div>
<div><br></div>
<div>Any<UITableView, ProtocolA> which is valid. </div>
<div><br></div>
<div>And by the way since the order in your proposal would matter,
this example won’t work at all, because its not:</div>
<div><br></div>
<div>Any<UITableView, Any<UIScrollView, Any<UIView,
ProtocolA>>> </div>
</div>
</blockquote>
<div><br></div>
<div>The order does <b>not</b> affect the semantic meaning of
the existential. There is a section in the proposal on how
existentials are conceptually 'reduced' from whatever form they
take when the programmer types them in, please read it. I am not
proposing a macro system. The compiler does not do textual
replacement in order to flatten nested existential
definitions.</div>
<div><br></div>
<div>This is also why it makes no sense to have a generic
"Any<T, U>", because such a type is identical to "Any<U,
T>", which is not true for any other generic type or aggregate
type in Swift.</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word">
<div><br></div>
In my proposal I explicitly banned multiple reference types and
inheritance branches like this. I would need to simplify that type
to Any<UITableView, ProtocolA> by myself.
<div>Ingeneral this is a good idea, but it makes nesting (with
typealiases) almost impossible, when there are some relationship
like in the above example.</div>
<div><span class=""><br></span></div>
<div><span class=""><br></span>
<div>
<div style="font-family:helvetica,arial;font-size:13px">
<span class="">-- <br>
Adrian Zubarev<br>
Sent with Airmail</span></div>
</div>
</div>
</div>
<br>
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<br></blockquote>
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