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// Both clang and gcc (in C++17 mode) complain about "invalid use of
incomplete type".
// But if all A's constructors are "=deleted", both clang and gcc compile
successfully.
// They don't need ANY constructor, yet try to instantiate them all.
// Is this somehow mandated by the standard, or simply a bug in both clang
and gcc?

template <typename T>
struct A
{
  using type = typenameT::type;
  A(type);
};

struct B;

A<B> func();
A<B> func2() { return func(); }

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<div dir=3D"ltr"><div class=3D""><span style=3D"color: rgb(0, 0, 255);" cla=
ss=3D"">// Both clang and gcc (in C++17 mode) complain about &quot;invalid =
use of incomplete type&quot;.<br></span></div><div class=3D""><span style=
=3D"color: rgb(0, 0, 255);" class=3D"">// But if all A&#39;s constructors a=
re &quot;=3Ddeleted&quot;, both clang and gcc compile successfully.<br></sp=
an></div><div class=3D""><span style=3D"color: rgb(0, 0, 255);" class=3D"">=
// They don&#39;t need ANY constructor, yet try to instantiate them all.</s=
pan></div><div class=3D""><span style=3D"color: rgb(0, 0, 255);" class=3D""=
>// Is this somehow mandated by the standard, or simply a bug in both clang=
 and gcc?</span></div><div class=3D""><span style=3D"color: rgb(0, 0, 255);=
" class=3D""></span></div><div class=3D""><span style=3D"color: rgb(0, 0, 2=
55);" class=3D""><br></span></div><div class=3D""><span style=3D"color: rgb=
(0, 0, 255);" class=3D"">template</span> &lt;<span style=3D"color: rgb(0, 0=
, 255);" class=3D"">typename</span> T&gt;</div><div class=3D""><span style=
=3D"color: rgb(0, 0, 255);" class=3D"">struct </span>A</div><div class=3D""=
>{</div><div class=3D""><span style=3D"color: rgb(0, 0, 255);" class=3D"">=
=C2=A0 using type =3D </span><span style=3D"color: rgb(0, 0, 255);" class=
=3D"">typename</span>T::type;</div><div class=3D"">=C2=A0 A(type);</div><di=
v class=3D"">};</div><br class=3D""><div class=3D""><span style=3D"color: r=
gb(0, 0, 255);" class=3D"">struct</span> B;</div><br class=3D""><div class=
=3D"">A&lt;B&gt; func();</div><div class=3D"">A&lt;B&gt; func2() {=C2=A0<sp=
an style=3D"color: rgb(0, 0, 255);" class=3D"">return </span>func(); }</div=
><div class=3D""><br></div></div>

<p></p>

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ls+unsubscribe@isocpp.org</a>.<br />
To post to this group, send email to <a href=3D"mailto:std-proposals@isocpp=
..org">std-proposals@isocpp.org</a>.<br />
To view this discussion on the web visit <a href=3D"https://groups.google.c=
om/a/isocpp.org/d/msgid/std-proposals/1dade9c8-f42d-4769-a9f0-16233e47327d%=
40isocpp.org?utm_medium=3Demail&utm_source=3Dfooter">https://groups.google.=
com/a/isocpp.org/d/msgid/std-proposals/1dade9c8-f42d-4769-a9f0-16233e47327d=
%40isocpp.org</a>.<br />

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