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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Ok, I guess I didn’t (don’t completely?) ‘get’ that there is a difference between “structured binding alias” and “reference”. Additionally, if you simply do
“auto”, you get copies, right? So those structured bindings actually introduce new variables, right?<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></a></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> James Dennett [mailto:james.dennett@gmail.com]
<br>
<b>Sent:</b> Wednesday, March 22, 2017 12:35 PM<br>
<b>To:</b> Keane, Erich <erich.keane@intel.com><br>
<b>Cc:</b> cfe-dev <cfe-dev@lists.llvm.org><br>
<b>Subject:</b> Re: [cfe-dev] Structured bindings seem to allow non-const references to a bitfield<o:p></o:p></span></p>
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<p class="MsoNormal">On Wed, Mar 22, 2017 at 12:01 PM, Keane, Erich via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org" target="_blank">cfe-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">I wasn't sure whether to bring this up here, or to bring it up on the reflector, but I'm not sure if this is a compiler issue or a standards issue. I read through the structured binding wording, and don't see anything one way or the other,
and GCC7 and Clang trunk both allow the following:<br>
<br>
struct F {<br>
unsigned a : 1;<br>
unsigned b : 2;<br>
unsigned c : 8;<br>
};<br>
<br>
int main() {<br>
F f;<br>
f.a = 0;<br>
f.b = 1;<br>
f.c = 4;<br>
<br>
auto &b = f.b; // correctly errors on non-const ref to a bitfield<br>
<br>
auto& [d,e,g] = f; // all are references to a bitfield<o:p></o:p></p>
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<p class="MsoNormal">The only reference here is an unnamed reference to `f`. None of `d`, `e`, `g` is a reference. `d` is another name for `f.a`, and similarly for `e` and `g`.<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"> d = 3; // Works, but warns about truncation<br>
c = 3; // Works, no diagnostic<br>
}<br>
<br>
Is this intended? Is this justified by the standard?<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal">The behavior you describe appears correct (and unsurprising to me), apart from the assumption that these are references; they're "structured bindings", not references.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">-- James<o:p></o:p></p>
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