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[basic.lookup.classref]p1 CWG 682: Should allow alias-templates followed by '<' #2593

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RealLitb opened this issue Dec 11, 2018 · 4 comments · Fixed by #3748
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[basic.lookup.classref]p1 CWG 682: Should allow alias-templates followed by '<' #2593

RealLitb opened this issue Dec 11, 2018 · 4 comments · Fixed by #3748
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cwg Issue must be reviewed by CWG. not-editorial Issue is not deemed editorial; the editorial issue is kept open for tracking.

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@RealLitb
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RealLitb commented Dec 11, 2018 •
edited

The text currently renders this ill-formed, because "c.U" in the context of the postfix expression doesn't find 'U' as a class-template, but alias template:

   struct C { typedef C type; int dummy; };

   template<typename>
   using U = C;

   int main() {
       C c;
       c.U<void>::dummy = 0;
   }

GCC and Clang implement the obvious, so I suspect this can be fixed editorially (stealing the wording used for "only-templates-that-yield-types::something" lookup).
@jensmaurer
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@RealLitb, Could you please edit your submission so that the angular brackets are visible?

@jensmaurer jensmaurer added changes requested Changes to the wording or approach have been requested and not yet applied. and removed changes requested Changes to the wording or approach have been requested and not yet applied. labels Dec 14, 2018
@jensmaurer
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Asked CWG whether to proceed editorially here; this feels like a normative change: http://lists.isocpp.org/core/2018/12/5331.php

@jensmaurer jensmaurer added the cwg Issue must be reviewed by CWG. label Dec 19, 2018
@jensmaurer
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A more involved example with a dependent object expression shows implementation variance. This is not editorial.

@jensmaurer jensmaurer added the not-editorial Issue is not deemed editorial; the editorial issue is kept open for tracking. label Dec 19, 2018
@jensmaurer jensmaurer changed the title [basic.lookup.classref]p1 Should allow alias-templates followed by '<' [basic.lookup.classref]p1 CWG 682: Should allow alias-templates followed by '<' Jun 14, 2019
@JohelEGP
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[Accepted as a DR at the July, 2019 meeting.]

@jensmaurer jensmaurer mentioned this issue Dec 29, 2020
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LWG Poll 2: P2051R0 C++ Standard Library Issues to be moved in Prague cplusplus/draft
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@RealLitb @JohelEGP @jensmaurer