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<div name="messageBodySection" style="font-size: 14px; font-family: -apple-system, BlinkMacSystemFont, sans-serif;">Hi,
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<div>I found a very rare situation that closure can’t infer the type of its parameter. See the code below:</div>
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<div><font face="Menlo" size="2"><span style="background-color: rgb(255, 255, 255);">```</span></font></div>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);"><span style="color: #ba2da2">func</span> withReference<T, Result>(<span style="color: #ba2da2">_</span> value: <span style="color: #ba2da2">inout</span> <span style="color: #4f8187">T</span>, <span style="color: #ba2da2">_</span> execute: (<span style="color: #ba2da2">inout</span> <span style="color: #4f8187">T</span>) <span style="color: #ba2da2">throws</span> -> <span style="color: #4f8187">Result</span>) <span style="color: #ba2da2">rethrows</span> -> <span style="color: #4f8187">Result</span> {</p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);">    <span style="color: #ba2da2">return</span> <span style="color: #ba2da2">try</span> execute(&value)</p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);">}</p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);"><span style="color: #ba2da2">struct</span> Person {</p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);">    <span style="color: #ba2da2">var</span> name: <span style="color: #703daa">String</span></p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);">}</p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);"><span style="color: #ba2da2">var</span> p = <span style="color: #4f8187">Person</span>(name: <span style="color: #d12f1b">"a"</span>)</p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo; color: rgb(49, 89, 93); background-color: rgb(255, 255, 255);">withReference<span style="color: #000000">(&</span><span style="color: #4f8187">p</span><span style="color: #000000">) { (v) </span> <span style="color: #ba2da2">in</span></p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);">    v.<span style="text-decoration: underline">n</span>ame = <span style="color: #d12f1b">"1"</span></p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);">}</p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo; color: rgb(62, 30, 129); background-color: rgb(255, 255, 255);">print<span style="color: #000000">(</span><span style="color: #4f8187">p</span><span style="color: #000000">)</span></p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);">```</p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);">The code can be compiled and produce correct result in Swift 3(Xcode 8) playground, but it can’t be compiled in Swift 4(Xcode 9 beta2).</p>
<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);">The error says: </p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo;"><span style="font-variant-ligatures: no-common-ligatures"><b>error: bug.playground:11:7: error: type of expression is ambiguous without more context</b></span></p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo;"><span style="font-variant-ligatures: no-common-ligatures"><b>    v.name = "1"</b></span></p>
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<p style="margin: 0px; font-size: 12px; line-height: normal; font-family: Menlo;"><span style="font-variant-ligatures: no-common-ligatures"><b>    ~~^~~~</b></span></p>
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<font face="Menlo" size="2">Is this related to exclusive access rule introduced to Swift 4?</font></div>
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Regards,<br />
Yilei He</div>
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