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808. §[forward] incorrect redundant specification

Section: 22.2.4[forward]Status:CD1Submitter: Jens MaurerOpened: 2008-03-13Last modified: 2016-02-01

Priority:Not Prioritized

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Discussion:

p4 (forward) says:

Return type: IfT is an lvalue-reference type, an lvalue; otherwise, an rvalue.

First of all, lvalue-ness and rvalue-ness are properties of an expression,not of a type (see 7.2.1[basic.lval]). Thus, the phrasing "Return type" is wrong.Second, the phrase says exactly what the core language wording says forfolding references in 13.4.2[temp.arg.type]/p4 and for function return valuesin 7.6.1.3[expr.call]/p10. (If we feel the wording should be retained, it shouldat most be a note with cross-references to those sections.)

The prose after the example talks about "forwarding as anint& (an lvalue)" etc.In my opinion, this is a category error: "int&" is a type, "lvalue" is aproperty of an expression, orthogonal to its type. (Btw, expressions cannothave reference type, ever.)

Similar with move:

Return type: an rvalue.

is just wrong and also redundant.

Proposed resolution:

Change 22.2.4[forward] as indicated:

template <class T> T&& forward(typename identity<T>::type&& t);

...

Return type: IfT is an lvalue-reference type, an lvalue; otherwise, an rvalue.

...

-7- In the first call tofactory,A1 is deduced asint, so 2 is forwarded toA's constructorasanint&& (an rvalue). In the second call to factory,A1 is deducedasint&, soi is forwarded toA's constructor asanint& (an lvalue).In both cases,A2 is deduced as double, so 1.414 is forwarded toA's constructor asdouble&& (an rvalue).

template <class T> typename remove_reference<T>::type&& move(T&& t);

...

Return type: an rvalue.