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Hello.

I have found this discussion that occured a while ago about std::identity
(a function object that just returns the passed argument) :
https://groups.google.com/forum/?fromgroups=#!topic/comp.std.c++/rG-zb2013TI
It would be very useful to have such a function object in the standard.
I would like to know what is the current status of this function object,
whether some paper were posted on it, and if not, why ?

Thanks.


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Hello.<br><br>I have found this discussion that occured a while ago about s=
td::identity (a function object that just returns the passed argument) : ht=
tps://groups.google.com/forum/?fromgroups=3D#!topic/comp.std.c++/rG-zb2013T=
I<br>It would be very useful to have such a function object in the standard=
..<br>I would like to know what is the current status of this function objec=
t, whether some paper were posted on it, and if not, why ?<br><br>Thanks.<b=
r><br><br>

<p></p>

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.

On Mar 4, 2013, at 8:40 AM, VinceRev <vince.rev@gmail.com> wrote:

> Hello.
>=20
> I have found this discussion that occured a while ago about std::identity=
 (a function object that just returns the passed argument) : https://groups=
..google.com/forum/?fromgroups=3D#!topic/comp.std.c++/rG-zb2013TI
> It would be very useful to have such a function object in the standard.
> I would like to know what is the current status of this function object, =
whether some paper were posted on it, and if not, why ?

std::identity was proposed in http://www.open-std.org/jtc1/sc22/wg21/docs/p=
apers/2005/n1856.html and was subsequently voted into the WP in http://www.=
open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2284.pdf.

The chief motivation for introducing std::identity in 2005/2007 was for the=
 specification of std::forward.  However soon after its introduction, issue=
s began to crop up with identity, starting with conflicts to pre-C++98 defi=
nitions of std::identity appearing as extensions:

http://cplusplus.github.com/LWG/lwg-defects.html#700
http://cplusplus.github.com/LWG/lwg-defects.html#823
http://cplusplus.github.com/LWG/lwg-defects.html#939

By the time LWG 939 was opened in 2008 forward itself had gone through seve=
ral revisions and no longer needed identity in its specification.  I person=
ally came to believe that std::identity had become more trouble than it was=
 worth, and recommended removing it.  It was finally removed from the WP in=
 2010 using LWG 939:

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3090.pdf

Howard

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