<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div></div><div><br></div><div><br>On Jun 30, 2017, at 1:48 AM, Adrian Zubarev via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br><br></div><blockquote type="cite"><div><style>
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.error { color:#AA0000; }</style><div class="bloop_markdown"><p>Well as Jordan Rose said on the linked SR, option (1) will probably never happen. Option (3) only makes sense if all of the options are supported (in that case there wouldn’t be any need for explicit <code>@autoclosure</code>, which could simply be merged into the closure type), or (2) is NOT supported so that one could pass a default autoclosure.</p>
<p>It leaves us only with (2), which is potentially a (small) breaking change, but it also feels more like a fix. I cannot imagine anyone is wrapping whole closures with auto closure, nor do I think a ‘convenience’ operation should disable the explicit ability to pass in a closure with the same signature. The latter feels like a bug. Furthermore I think most code that relies on this is already doing something like.</p>
<pre><code class="swift">func bar(_ closure: @autoclosure () -> Int) { foo(closure)}
func foo(_ closure: () -> Int)
</code></pre>
<p>But this is only an assumption of mine.</p>
<p>Theoretically it suppose to work the other way around, right? Again <code>@autoclosure</code> supposed to be a syntactical convenience feature which implies that it won’t disable *too* much from the closure type. Disallowing arguments is logical consequence but not the other issues I mentioned here and in the SR.</p>
<p>—</p>
<p>One question: Do we need to go through a full evolution process for pitch (2) or is a bug report enough here?</p></div></div></blockquote><div>Surely the former—I'm fully against this change, and imagine others are also. Autoclosure exists to provide opt-in lazy evaluation of values by wrapping them in a closure. I think it's semantically incorrect to accept an already wrapped value here, and adding this sort of implicit conversion can introduce potential ambiguity when used with generic functions.</div><div><br></div><div>Very large -1.</div><blockquote type="cite"><div><div class="bloop_markdown">
<p></p></div><div class="bloop_original_html"><style>body{font-family:Helvetica,Arial;font-size:13px}</style><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> <br> <div id="bloop_sign_1498806914384722944" 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 30. Juni 2017 um 00:59:45, Beta (<a href="mailto:rwidmann@apple.com">rwidmann@apple.com</a>) schrieb:</p> <blockquote type="cite" class="clean_bq"><span><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div></div><div>
<title></title>
<div class="">These are all interesting ideas at first blush, but
introduce some oddities into the type system</div>
<div class=""><br class=""></div>
1. We accept this 😳. If we were to take this as an official
language change it would mean that we would allow coercing T to (_)
-> T by emitting a closure that takes an argument list (of arity
given by the contextual type) that we throw away anyways. I
would <i class="">much</i> prefer we diagnose this instead.
@autoclosure is a syntactically convenient way to ask for
laziness - that’s it.
<div class=""><br class="">
<div class="">2. Doing this collapses overloads on
@autoclosure</div>
<div class=""><br class=""></div>
<div class="">
<div style="margin: 0px; font-stretch: normal; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="color: #ba2da2" class="">func</span>
foo(<span style="color: #ba2da2" class="">_</span> f : <span style="color: #ba2da2" class="">@autoclosure</span> () -> <span style="color: #703daa" class="">String</span>) {}</div>
<div style="margin: 0px; font-stretch: normal; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="color: #ba2da2" class="">func</span>
foo(<span style="color: #ba2da2" class="">_</span> f : () ->
<span style="color: #703daa" class="">String</span>) {}</div>
<div class=""><br class=""></div>
<div class=""><br class=""></div>
<div class="">Which is fine by me except for the code you would
break that relies on this. I don’t see a reasonable migration
path here - perhaps you have one in mind.</div>
<div class=""><br class=""></div>
<div class="">3. @autoclosure is a parameter attribute.
Allowing it to appear in other positions is redundant and
doesn’t actually accomplish anything outside of maintaining
consistency with the first point.</div>
<div class=""><br class=""></div>
<div class="">I hope I don’t come off as too harsh. It’s just
a little shocking to me that we accept the code in the linked
SR.</div>
<div class=""><br class=""></div>
<div class="">~Robert Widmann</div>
<div><br class="">
<blockquote type="cite" class="">
<div class="">On Jun 24, 2017, at 9:10 AM, Adrian Zubarev via
swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div class="bloop_markdown" 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; -webkit-text-stroke-width: 0px; background-color: rgb(254, 254, 254);">
<p style="margin: 15px 0px; -webkit-margin-before: 0px;" class="">
Hello folks,</p>
<p style="margin: 15px 0px;" class="">Here is a quick and
straightforward pitch about<span class="Apple-converted-space"> </span><code style="font-family: Menlo, Consolas, "Liberation Mono", Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 1px solid rgb(234, 234, 234); margin: 0px 2px; padding: 0px 5px; word-break: normal; word-wrap: normal; -webkit-margin-before: 0px;" class="">@autoclosure</code>. Currently the attribute indicates
that the caller has to pass an expression so that the braces can be
omitted. This is a convenient behavior only, but it also has it’s
shortcomings.</p>
<p style="margin: 15px 0px;" class="">I would like to propose an
extension of that behavior.</p>
<div class="bloop_markdown"><br style="-webkit-margin-before: 0px;" class=""></div>
1. Allow access to arguments and shorthand argument
names:<br class="">
<ol style="margin: 15px 0px;" class=""></ol>
<pre style="margin: 15px 0px; font-family: Menlo, Consolas, "Liberation Mono", Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 1px solid rgb(204, 204, 204); overflow: auto; padding: 4px 8px; word-break: normal; word-wrap: normal;" class=""><code class="swift" style="font-family: Menlo, Consolas, "Liberation Mono", Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 0px; margin: 0px; padding: 0px; word-break: normal; word-wrap: normal; -webkit-margin-before: 0px;">// Bug: <a href="https://bugs.swift.org/browse/SR-5296" style="color: rgb(65, 131, 196); background-color: inherit; text-decoration: none; -webkit-margin-before: 0px;" class="">https://bugs.swift.org/browse/SR-5296</a>
func foo(_ test: @autoclosure (Int) -> Int = { $0 }) {
print(test(42))
}
// Convenient access using shorthand arguments
foo(Int(Double($0) * 3.14)))
</code></pre>
<div class="bloop_markdown"><br style="-webkit-margin-before: 0px;" class=""></div>
2. Make<span class="Apple-converted-space"> </span><code style="font-family: Menlo, Consolas, "Liberation Mono", Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 1px solid rgb(234, 234, 234); margin: 0px 2px; padding: 0px 5px; word-break: normal; word-wrap: normal;" class="">@autoclosure</code><span class="Apple-converted-space"> </span>only wrap when
necessary:<br class="">
<ol style="margin: 15px 0px;" class=""></ol>
<pre style="margin: 15px 0px; font-family: Menlo, Consolas, "Liberation Mono", Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 1px solid rgb(204, 204, 204); overflow: auto; padding: 4px 8px; word-break: normal; word-wrap: normal;" class=""><code class="swift" style="font-family: Menlo, Consolas, "Liberation Mono", Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 0px; margin: 0px; padding: 0px; word-break: normal; word-wrap: normal; -webkit-margin-before: 0px;">func bar(_ test: @autoclosure () -> Int) {
print(test())
}
let test = { 42 }
// function produces expected type 'Int'; did you mean to call it with '()'?
bar(test)
</code></pre>
<div class="bloop_markdown"><br style="-webkit-margin-before: 0px;" class=""></div>
3. Extend<span class="Apple-converted-space"> </span><code style="font-family: Menlo, Consolas, "Liberation Mono", Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 1px solid rgb(234, 234, 234); margin: 0px 2px; padding: 0px 5px; word-break: normal; word-wrap: normal;" class="">@autoclosure</code><span class="Apple-converted-space"> </span>to closure types in general
(this change is for consistent alignment):</div>
<div class="bloop_markdown" 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; -webkit-text-stroke-width: 0px; background-color: rgb(254, 254, 254);">
<ol style="margin: 15px 0px; -webkit-margin-before: 0px;" class="">
</ol>
<pre style="margin: 15px 0px; font-family: Menlo, Consolas, "Liberation Mono", Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 1px solid rgb(204, 204, 204); overflow: auto; padding: 4px 8px; word-break: normal; word-wrap: normal;" class=""><code class="swift" style="font-family: Menlo, Consolas, "Liberation Mono", Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 0px; margin: 0px; padding: 0px; word-break: normal; word-wrap: normal; -webkit-margin-before: 0px;">// Note how we're using the shorthand argument list for this expression
let uppercaseWrapper: @autoclosure (String) -> String = $0.uppercased()
</code></pre>
<div style="margin: 15px 0px;" class=""><br class="webkit-block-placeholder"></div>
</div>
<div class="bloop_original_html" 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; -webkit-text-stroke-width: 0px; background-color: rgb(254, 254, 254);">
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<br class="">
<div id="bloop_sign_1498319089122447872" class="bloop_sign">
<div style="font-family: helvetica, arial; font-size: 13px;" class="">-- <br class="">
Adrian Zubarev<br class="">
Sent with Airmail</div>
</div>
</div>
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</blockquote>
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</div></div></span></blockquote></div><div class="bloop_markdown"><p></p></div></div></blockquote><blockquote type="cite"><div><span>_______________________________________________</span><br><span>swift-evolution mailing list</span><br><span><a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a></span><br><span><a href="https://lists.swift.org/mailman/listinfo/swift-evolution">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br></div></blockquote></body></html>