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P0849R8 auto(x): decay-copy in the language #5015

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Merged
merged 1 commit into from
Oct 19, 2021
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P0849R8 auto(x): decay-copy in the language #5015

merged 1 commit into from
Oct 19, 2021

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jensmaurer
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@jensmaurer jensmaurer commented Oct 8, 2021 •
edited by tkoeppe
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@jensmaurer jensmaurer added this to the post-2021-10 milestone Oct 8, 2021
JohelEGP
JohelEGP suggested changes Oct 9, 2021
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@jensmaurer jensmaurer added the changes requested Changes to the wording or approach have been requested and not yet applied. label Oct 14, 2021
@jensmaurer jensmaurer force-pushed the motions-2021-10-lwg-8 branch from fa0f838 to 5195041 Compare October 15, 2021 10:49
@jensmaurer jensmaurer removed the changes requested Changes to the wording or approach have been requested and not yet applied. label Oct 15, 2021
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@opensdh, please have a look.

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opensdh commented Oct 15, 2021

Why me in this case?

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Why me in this case?

Because you wanted it: #4745

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opensdh commented Oct 15, 2021

Thanks for the reminder!

timsong-cpp
timsong-cpp reviewed Oct 16, 2021
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@jensmaurer jensmaurer added the changes requested Changes to the wording or approach have been requested and not yet applied. label Oct 16, 2021
burblebee
burblebee approved these changes Oct 16, 2021
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@jensmaurer jensmaurer force-pushed the motions-2021-10-lwg-8 branch from 5195041 to c782a12 Compare October 18, 2021 20:19
@jensmaurer jensmaurer removed the changes requested Changes to the wording or approach have been requested and not yet applied. label Oct 18, 2021
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@opensdh, could you please have a look at the clean-up patch implementing your suggestion from #4745? Thanks.

@tkoeppe tkoeppe force-pushed the motions-2021-10-lwg-8 branch from c782a12 to 612d068 Compare October 19, 2021 22:11
tkoeppe
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source/declarations.tex Outdated
@@ -1954,6 +1954,20 @@
that contains a placeholder type,
\tcode{T} is the declared type of the non-type template parameter
and $E$ is the corresponding template argument.
\item
For an explicit type conversion\iref{expr.type.conv},
\tcode{T} is \tcode{auto}.
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So as to not just say "T is auto" without any hint why, @zygoloid suggests something like this:

[...] T is the specified type. [Note: Placeholder type deduction is only performed when the specified type is auto. --end note]

It's a bit more verbose, but helps the reader along a little. What do you think, @opensdh, @jensmaurer ?

Alternatively, for an even more radical change, see second comment.

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Moving discussion to separate pull request #5039.

tkoeppe
tkoeppe reviewed Oct 19, 2021
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source/expressions.tex Outdated
Comment on lines 3356 to 3358
Otherwise, if the type is \tcode{auto},
it is replaced by the type deduced for the variable \tcode{x}
in the invented declaration\iref{dcl.spec.auto},
which is never interpreted as a function declaration:
\begin{codeblock}
auto x @\placeholder{init}@;
\end{codeblock}
, where \placeholder{init} is the initializer.
it is replaced by the type
determined by placeholder type deduction\iref{dcl.type.auto.deduct}.
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Even more radical alternative:

Otherwise, if the type contains a placeholder type, it is replaced by the type
determined by placeholder type deduction\iref{dcl.type.auto.deduct}.

And then move the "shall" up to dcl.type.auto.deduct:

For an explicit type conversion, T is the specified type, which shall be auto.

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I agree with this direction (as implemented in #5039).

@tkoeppe tkoeppe mentioned this pull request Oct 19, 2021
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@tkoeppe tkoeppe force-pushed the motions-2021-10-lwg-8 branch from 612d068 to 4e228b7 Compare October 19, 2021 22:55
@tkoeppe tkoeppe merged commit b9b0477 into main Oct 19, 2021
@jensmaurer jensmaurer deleted the motions-2021-10-lwg-8 branch July 29, 2022 07:31
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[2021-10 LWG Motion 8] P0849R8 auto(x): decay-copy in the language P0849 auto(x): DECAY_COPY in the language
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@jensmaurer @opensdh @tkoeppe @burblebee @timsong-cpp @JohelEGP