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From: Alexander Zaitsev <zamazan4ik@gmail.com>
Newsgroups: gmane.comp.lang.c++.isocpp.proposals
Subject: Re: [idea for proposal] Adding std::shift to <algorithm>
Date: Wed, 12 Jul 2017 04:18:02 -0700 (PDT)
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Hello.

Really nice idea! But i have some suggestions:
* shift should return iterator (or two)
* it should be constexpr

Also i suggest you create PR to Boost.Algorithm (or we can work together -=
=20
i will help you as mush as possible). And after including into=20
Bost.Algorithm we can write proposal to C++ Standard.

=D1=81=D1=80=D0=B5=D0=B4=D0=B0, 12 =D0=B8=D1=8E=D0=BB=D1=8F 2017 =D0=B3., 1=
2:53:19 UTC+3 =D0=BF=D0=BE=D0=BB=D1=8C=D0=B7=D0=BE=D0=B2=D0=B0=D1=82=D0=B5=
=D0=BB=D1=8C d...@soundradix.com=20
=D0=BD=D0=B0=D0=BF=D0=B8=D1=81=D0=B0=D0=BB:
>
> Hi,
>
> Would anyone be interested in adding std::shift to <algorithm>?=20
>
> It would be similar to both:
> - std::rotate, but without moving the head elements back to the tail. Thi=
s=20
> would allow a more efficient implementation and clearer semantics in case=
=20
> rotation is not needed as well as correctness in case rotation is undesir=
ed.
> - <algorithm>'s std::move/std::move_backward (depending on the shift=20
> direction).
>
> std::shift should probably accommodate both left and right shifts by one=
=20
> of:
> - giving it either begin() and end(), or rbegin() and rend(), similar to=
=20
> how std::rotate works for both left and right rotations. The advantage is=
=20
> compactness of the implementation.
> - allowing the shift count parameter to be either positive or negative.=
=20
> The advantage is compactness, though it might not be clear which directio=
n=20
> is which - to be consistent with rotate, positive integers should shift t=
o=20
> the left.
> - having std::shift_right and std::shift_left functions. The advantage is=
=20
> clarity when calling the methods, although the same argument could be mad=
e=20
> for having separate std::rotate_left and std::rotate_right instead of=20
> std::rotate, which we don't have.
>
> Here's a sample implementation of a shift to the right direction:
>
> template<class BidirIt>=20
> void shift_right(BidirIt first, BidirIt last, unsigned int n =3D 1)=20
> {=20
>     std::move_backward(first, last - n, last);=20
> }
>
> This demonstrates that while std::shift is implementable with=20
> std::move/std::move_backward,
> 1) It isn't immediately clear from the code (at least to my eyes) that=20
> this is a shift right, unless you are intimately familiar with=20
> std::move_backward.
> 2) Different calls, either to std::move or to std::move_backward, are=20
> required, depending on the shift direction.
>
> So, implementing std::shift would allow writing more readable code.
>
> Thanks,
> Dan
>

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<div dir=3D"ltr">Hello.<div><br></div><div>Really nice idea! But i have som=
e suggestions:</div><div>* shift should return iterator (or two)</div><div>=
* it should be constexpr</div><div><br></div><div>Also i suggest you create=
 PR to Boost.Algorithm (or we can work together - i will help you as mush a=
s possible). And after including into Bost.Algorithm we can write proposal =
to C++ Standard.<br><br>=D1=81=D1=80=D0=B5=D0=B4=D0=B0, 12 =D0=B8=D1=8E=D0=
=BB=D1=8F 2017 =D0=B3., 12:53:19 UTC+3 =D0=BF=D0=BE=D0=BB=D1=8C=D0=B7=D0=BE=
=D0=B2=D0=B0=D1=82=D0=B5=D0=BB=D1=8C d...@soundradix.com =D0=BD=D0=B0=D0=BF=
=D0=B8=D1=81=D0=B0=D0=BB:<blockquote class=3D"gmail_quote" style=3D"margin:=
 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"><div =
dir=3D"ltr">Hi,<div><br></div><div>Would anyone be interested in adding std=
::shift to &lt;algorithm&gt;?=C2=A0</div><div><br></div><div>It would be si=
milar to both:</div><div>- std::rotate, but without moving the head element=
s back to the tail. This would allow a more efficient implementation and cl=
earer semantics in case rotation is not needed as well as correctness in ca=
se rotation is undesired.</div><div>- &lt;algorithm&gt;&#39;s std::move/std=
::move_backward (depending on the shift direction).</div><div><br></div><di=
v>std::shift should probably accommodate both left and right shifts by one =
of:</div><div>- giving it either begin() and end(), or rbegin() and rend(),=
 similar to how std::rotate works for both left and right rotations. The ad=
vantage is compactness of the implementation.</div><div>- allowing the shif=
t count parameter to be either positive or negative. The advantage is compa=
ctness, though it might not be clear which direction is which - to be consi=
stent with rotate, positive integers should shift to the left.<br></div><di=
v><div>- having std::shift_right and std::shift_left functions. The advanta=
ge is clarity when calling the methods, although the same argument could be=
 made for having separate std::rotate_left and std::rotate_right instead of=
 std::rotate, which we don&#39;t have.</div></div><div><br></div><div>Here&=
#39;s a sample implementation of a shift to the right direction:</div><br><=
div style=3D"background-color:rgb(250,250,250);border:1px solid rgb(187,187=
,187);word-wrap:break-word"><code><div><span style=3D"color:#008">template<=
/span><span style=3D"color:#660">&lt;</span><span style=3D"color:#008">clas=
s</span><span style=3D"color:#000"> </span><span style=3D"color:#606">Bidir=
It</span><span style=3D"color:#660">&gt;</span><span style=3D"color:#000"> =
<br></span><span style=3D"color:#008">void</span><span style=3D"color:#000"=
> shift_right</span><span style=3D"color:#660">(</span><span style=3D"color=
:#606">BidirIt</span><span style=3D"color:#000"> first</span><span style=3D=
"color:#660">,</span><span style=3D"color:#000"> </span><span style=3D"colo=
r:#606">BidirIt</span><span style=3D"color:#000"> </span><span style=3D"col=
or:#008">last</span><span style=3D"color:#660">,</span><span style=3D"color=
:#000"> </span><span style=3D"color:#008">unsigned</span><span style=3D"col=
or:#000"> </span><span style=3D"color:#008">int</span><span style=3D"color:=
#000"> n </span><span style=3D"color:#660">=3D</span><span style=3D"color:#=
000"> </span><span style=3D"color:#066">1</span><span style=3D"color:#660">=
)</span><span style=3D"color:#000"> <br></span><span style=3D"color:#660">{=
</span><span style=3D"color:#000"> <br>=C2=A0 =C2=A0 std</span><span style=
=3D"color:#660">::</span><span style=3D"color:#000">move_backward</span><sp=
an style=3D"color:#660">(</span><span style=3D"color:#000">first</span><spa=
n style=3D"color:#660">,</span><span style=3D"color:#000"> </span><span sty=
le=3D"color:#008">last</span><span style=3D"color:#000"> </span><span style=
=3D"color:#660">-</span><span style=3D"color:#000"> n</span><span style=3D"=
color:#660">,</span><span style=3D"color:#000"> </span><span style=3D"color=
:#008">last</span><span style=3D"color:#660">);</span><span style=3D"color:=
#000"> <br></span><span style=3D"color:#660">}</span><span style=3D"color:#=
000"><br></span></div></code></div><div><br></div><div>This demonstrates th=
at while std::shift is implementable with std::move/std::move_backward,</di=
v><div>1) It isn&#39;t immediately clear from the code (at least to my eyes=
) that this is a shift right, unless you are intimately familiar with std::=
move_backward.</div><div>2) Different calls, either to std::move or to std:=
:move_backward, are required, depending on the shift direction.</div><div><=
br></div><div>So, implementing std::shift would allow writing more readable=
 code.</div><div><br></div><div>Thanks,</div><div>Dan</div></div></blockquo=
te></div></div>

<p></p>

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