<html><head><style>body{font-family:Helvetica,Arial;font-size:13px}</style></head><body style="word-wrap:break-word"><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 invite you to read the proposal rules again with a fresh mindset and benevolence spirit.</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">It’s my first one and may not be very clear but the rules are straightforward.</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">Especially try to forget that Void is a tuple or anything. </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">Void is Nothing in the programmer’s mind. An instance of Void shouldn’t even exist.</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">The proposed meaning of Void is to be a “lack” of arguments. It means that each “Void” argument reduces the arity of the function by one, at its exact position. Especially look at the canonical signature definition, and the proposed rules of reduction.</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">That proposal, if implemented, would effectively allow `Callback<Void>` to be called without arguments in the context of swift4.</div> <br> <div id="bloop_sign_1497298215942644224" class="bloop_sign"><div style="font-family:helvetica,arial;font-size:13px">—</div><div><font face="Helvetica" size="1">very short reply expected - <a href="http://vsre.info">vsre.info</a></font></div><div style="font-family:helvetica,arial;font-size:13px">Jérémie Girault<br></div></div> <br><p class="airmail_on">On 12 juin 2017 at 22:06:54, Xiaodi Wu (<a href="mailto:xiaodi.wu@gmail.com">xiaodi.wu@gmail.com</a>) wrote:</p> <blockquote type="cite" class="clean_bq"><span><div><div></div><div>
<title></title>
<div dir="ltr">On Mon, Jun 12, 2017 at 2:56 PM, Jérémie Girault
<span dir="ltr"><<a href="mailto:jeremie.girault@gmail.com" target="_blank">jeremie.girault@gmail.com</a>></span>
wrote:<br>
<div class="gmail_extra">
<div class="gmail_quote">
<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 id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
@Xiaodi Wu</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
Disagree, and we would need the original designer here to help us,
but my understanding of the original meaning of tuples-as-arguments
is that when I define:</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
`func foo(_ arg0: Any, _ arg1: Any) {}`</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
I can afterwards “apply” a tuple to a function named `foo` and
therefore execute the function on this tuple.</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
Calling a function syntax was equivalent to put a tuple next to a
function name:</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
`foo(42, “hello")` the left-hand is `foo`, the right-hand is `(42,
“hello")` is the tuple.</div>
<div id="m_-2321952076676033477bloop_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="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
The same way if I have</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
`func foo()`</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
`foo()` means calling `foo` with argument `()` and there we have
our original `Void`</div>
<div id="m_-2321952076676033477bloop_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="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
That meaning changed recently due to multiple SE implementations
actually.</div>
</div>
</blockquote>
<div><br></div>
<div>Tuples-as-arguments never shipped in any version of Swift, and
the ability to "apply" a tuple like that was removed by
SE-0029--the original goal was to implement this change in time for
Swift 2.2.</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 id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
The parenthesis around the call don't have a tuple meaning anymore.
Therefore it breaks a lot of code relying on this feature of the
language, which was quite elegant, but could not handle advanced
functions features.</div>
</div>
</blockquote>
<div><br></div>
<div>Yes, this is an intentional and approved part of SE-0029. The
drawbacks were enumerated in that proposal and were deemed
acceptable.</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 id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
@john: Void can happen easily in parameters due to generics, the
easiest example that breaks with swift4 is</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
`typealias Callback<T> = (T) -> Void`</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
here</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
`Callback<Void>` which is perfectly reasonable introduces
Void in the argument list and forces the caller to introduces an
empty partenthesis set when invoking:</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
```</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
let foo: Callback<Void> = { }</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
foo(())</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
```</div>
</div>
</blockquote>
<div><br></div>
<div>`Callback<T> = (T) -> Void` refers to a callback that
takes exactly one argument. Since argument lists are not tuples, it
is not possible to invoke such a callback with zero arguments, or
for that matter with two, three, four, or five arguments.</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 id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
</div>
<div id="m_-2321952076676033477bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
That’s were the proposal shines in my opinion: adapting the meaning
of Void to the current context of swift4 gives back the language
the elegant syntax it had while preserving the type system</div>
</div>
</blockquote>
<div><br></div>
<div>I'm not sure what you mean by this. No change in `Void` can
cause a function of type (T) -> Void to accept zero arguments:
it requires one argument of type T.</div>
<div><br></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 id="m_-2321952076676033477bloop_sign_1497296119954916864" class="m_-2321952076676033477bloop_sign">
<div style="font-family:helvetica,arial;font-size:13px">
<span class=""><span style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:small">On
12 juin 2017 at 20:04:18, Xiaodi Wu (</span><a href="mailto:xiaodi.wu@gmail.com" target="_blank" style="font-family:arial,sans-serif">xiaodi.wu@gmail.com</a><span style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:small">)
wrote:</span><br></span></div>
</div>
<div>
<div class="h5">
<blockquote type="cite" class="m_-2321952076676033477clean_bq">
<div>
<div>
<div><span>On Mon, Jun 12, 2017 at 12:44 Jérémie Girault
<<a href="mailto:jeremie.girault@gmail.com" target="_blank">jeremie.girault@gmail.com</a>> wrote:<br></span>
<div class="gmail_quote">
<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 id="m_-2321952076676033477m_5965133149641952769bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<p><span>Void was the empty tuple because arguments were
tuples.</span></p>
</div>
</div>
</blockquote>
<div><span><br></span></div>
<div><span>As John explained, that is _not_ correct. Void was not
motivated by anything to do with argument lists.</span></div>
<div><span><br></span></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 id="m_-2321952076676033477m_5965133149641952769bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<p><span>So no arguments meant empty tuple.</span></p>
<p><span>If we consider the empty tuple to be an argument, then the
type for the type of empty tuple should be `Unit`</span></p>
</div>
</div>
</blockquote>
<div><span><br></span></div>
<div><span>It has been suggested to rename Void to Unit. I do
believe it’s on the commonly rejected ideas list (and if it’s not,
it ought to be).</span></div>
<div><span><br></span></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 id="m_-2321952076676033477m_5965133149641952769bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<p><span>Void, however, seem naturally fitted for the absence of
argument.</span></p>
<p><span>Should `func foo(Void)` be different from `func
foo()`?</span></p>
</div>
</div>
</blockquote>
<div><span><br></span></div>
<div><span>SE-0110 determined that the two should in fact be
different.</span></div>
<div><span><br></span></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 id="m_-2321952076676033477m_5965133149641952769bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<p><span>I don’t think so. But different from `func foo(Unit)` ?
Yes !</span></p>
</div>
</div>
</blockquote>
<div><span><br></span></div>
<div><span>It sounds like your quarrel is with the name of the
typealias. I don’t see how that solves any issues with the loss of
tuple splatting. Functions will still return (), and you foo(()) is
not foo().</span></div>
<div><span><br></span></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 id="m_-2321952076676033477m_5965133149641952769bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<p><span>My point here is that we probably won’t have splatting for
swift4.</span></p>
<p><span><br></span></p>
</div>
<div id="m_-2321952076676033477m_5965133149641952769bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<span>But if we consider the type system as a guide, we can
consider 3 simple set of rules and restore almost 100% source
compatibility while keeping the improvement of SE-0110</span></div>
<div id="m_-2321952076676033477m_5965133149641952769bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<span>- Rules for swift3 tuples-arguments of cardinality zero
(Void) in swift 4 (this proposition)</span></div>
<div id="m_-2321952076676033477m_5965133149641952769bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<span>- Rules for swift3 tuples-arguments of cardinality one in
swift 4 (proposition to be done)</span></div>
<div id="m_-2321952076676033477m_5965133149641952769bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<span>- Rules for swift3 tuples-arguments of cardinality > 1 in
swift 4 (proposition to be done)</span></div>
</div>
<div style="word-wrap:break-word"><span><br></span>
<div id="m_-2321952076676033477m_5965133149641952769bloop_sign_1497288880940260864" class="m_-2321952076676033477m_5965133149641952769bloop_sign">
<div style="font-family:helvetica,arial;font-size:13px">
<span>—</span></div>
<div><span><font face="Helvetica" size="1">very short reply
expected - <a href="http://vsre.info" target="_blank">vsre.info</a></font></span></div>
<div style="font-family:helvetica,arial;font-size:13px">
<span>Jérémie Girault<br></span></div>
</div>
<span><br></span></div>
<div style="word-wrap:break-word">
<p class="m_-2321952076676033477m_5965133149641952769airmail_on">
<span>On 12 juin 2017 at 19:25:31, Xiaodi Wu (<a href="mailto:xiaodi.wu@gmail.com" target="_blank">xiaodi.wu@gmail.com</a>) wrote:</span></p>
<div>
<blockquote type="cite" class="m_-2321952076676033477m_5965133149641952769clean_bq" style="font-family:Helvetica,Arial;font-size:13px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<div>
<div>
<div><span><span>Unfortunately, I think this proposal appears to be
mistaken as to this key premise: Void was never (IIUC) meant to
model the absence of arguments; it is a type with one possible
value.</span></span></div>
</div>
</div>
</blockquote>
</div>
<div>
<div>
<blockquote type="cite" class="m_-2321952076676033477m_5965133149641952769clean_bq" style="font-family:Helvetica,Arial;font-size:13px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<div>
<div>
<div><span><br>
<br>
If I recall, a number of conversations have been raised about Void
being a typealias of (), and the definitive response has been that
this falls into the ship-has-sailed category of out-of-scope
changes.<br>
<br>
More generally, the recent spate of complaints about regressions to
a particular coding style have to do with loss of implicit tuple
splatting, the cure for which is a proper implementation of tuple
splatting, not poking holes into settled parts of the type
system.</span></div>
</div>
</div>
</blockquote>
</div>
<div>
<blockquote type="cite" class="m_-2321952076676033477m_5965133149641952769clean_bq" style="font-family:Helvetica,Arial;font-size:13px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<div>
<div>
<div><span><br class="m_-2321952076676033477m_5965133149641952769Apple-interchange-newline">
<br></span></div>
<div><span><br></span>
<div class="gmail_quote">
<div><span>On Mon, Jun 12, 2017 at 12:15 John McCall via
swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>>
wrote:<br></span></div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">
<div style="word-wrap:break-word"><span><br></span>
<div>
<blockquote type="cite">
<div><span>On Jun 12, 2017, at 4:48 AM, Jérémie Girault via
swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>>
wrote:</span></div>
<span><br class="m_-2321952076676033477m_5965133149641952769m_7884169765734884326m_-2000047954192297274Apple-interchange-newline">
</span>
<div>
<div id="m_-2321952076676033477m_5965133149641952769m_7884169765734884326m_-2000047954192297274bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;margin:0px">
<span>Hi here,</span></div>
<div id="m_-2321952076676033477m_5965133149641952769m_7884169765734884326m_-2000047954192297274bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;margin:0px">
<span><br></span></div>
<div id="m_-2321952076676033477m_5965133149641952769m_7884169765734884326m_-2000047954192297274bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;margin:0px">
<span>As I tested swift4 in xcode9b1 I noticed a lot of regressions
about tuples usage.</span></div>
<div id="m_-2321952076676033477m_5965133149641952769m_7884169765734884326m_-2000047954192297274bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;margin:0px">
<span><br></span></div>
<div id="m_-2321952076676033477m_5965133149641952769m_7884169765734884326m_-2000047954192297274bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;margin:0px">
<span>After documenting myself about the changes which happened, I
thought that they could be improved. Instead of fighting these
propositions (which make sense), I wanted create a few proposal
which would improve these recent changes with a few simple
rules.</span></div>
<div id="m_-2321952076676033477m_5965133149641952769m_7884169765734884326m_-2000047954192297274bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;margin:0px">
<span><br></span></div>
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<span>My propositions are based on the recent decisions and in the
continuation of SE-0110. The first one is about Void.</span></div>
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<span>Void is historically defined as the type of the empty tuple.
The reason of this is that arguments were initially considered as
tuple.</span></div>
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<div><span>The dominant consideration here was always return types,
not parameters. I'm not sure there was ever much point in
writing Void in a parameter list, but whatever reasons there were
surely vanished with SE-0066.</span></div>
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<div><span>Note that 'void' in C was originally exclusively a
return type. ANSI gave it a new purpose it with void*, but
the meaning is totally unrelated.</span></div>
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<div><span>John.</span></div>
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