Talk:Decltype

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	Decltype has been listed as one of the Engineering and technology good articles under the good article criteria. If you can improve it further, please do so. If it no longer meets these criteria, you can reassess it.
Article milestones Date Process Result November 9, 2009 Good article nominee Listed December 4, 2023 Good article reassessment Kept
	A fact from this article appeared on Wikipedia's Main Page in the "Did you know?" column on September 9, 2009. The text of the entry was: Did you know ... that decltype can be used to "clean up function syntax mess" in C++ programming?
Current status: Good article

There should be a section here on the problem of decltype causing functions to accidentally return references to temporaries. Example:

template<typename T> auto f(bool b, T t, T u) -> decltype(b ? t : u) { return b ? t : u; }

Here, decltype(b ? t : u) will be T &, and this function will return a dangling reference. Does anyone have a citation for the appropriate critique? 74.125.122.49 (talk) 16:55, 5 January 2012 (UTC)Reply

No mention of declval within article. Nor does there exist a wiki page for same. — Preceding unsigned comment added by 46.65.52.44 (talk) 19:51, 5 November 2012 (UTC)Reply

That's because there is no such thing. — Preceding unsigned comment added by 192.35.35.35 (talk) 17:01, 31 May 2013 (UTC)Reply

Oh, but there is. It resides in the <utility> header (defined as template<typename T> typename std::add_rvalue_reference<T>::type declval() or similar). It seems no one has found the time to cover declval in this article, and it almost certainly doesn't warrant a stand-alone article. Regards, decltype (talk) 10:29, 4 June 2013 (UTC)Reply

It should be mentioned by some examples. And decltype(auto) should be explained. --2A02:2028:2A7:C1B0:C89B:DE41:D2DA:146E (talk) 09:21, 25 August 2014 (UTC)Reply

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The first sentence is a bit misleading:

In the C++ programming language, decltype is a keyword used to query the type of an expression.

I suggest rephrasing along the lines of "... query the type of a variable declaration or expression, depending on the argument."

Beginners often get burned by the fact that C++ uses one keyword for two different purposes, so introducing the keyword as if it's possible to understand it as a single concept can compound the problem.

Wikweb (talk) 18:36, 14 June 2021 (UTC)Reply