Hi,

Would anyone be interested in addin= g std::shift to <algorithm>?=C2=A0

It would = be similar to both:

- std::rotate, but without moving the head el= ements back to the tail. This would allow a more efficient implementation a= nd clearer semantics in case rotation is not needed as well as correctness = in case rotation is undesired.

- <algorithm>'s std::mov= e/std::move_backward (depending on the shift direction).

std::shift should probably accommodate both left and right shifts by= one of:

- giving it either begin() and end(), or rbegin() and re= nd(), similar to how std::rotate works for both left and right rotations. T= he advantage is compactness of the implementation.

- allowing the= shift count parameter to be either positive or negative. The advantage is = compactness, though it might not be clear which direction is which - to be = consistent with rotate, positive integers should shift to the left.

- having std::shift_right and std::shift_left functions. The ad= vantage is clarity when calling the methods, although the same argument cou= ld be made for having separate std::rotate_left and std::rotate_right inste= ad of std::rotate, which we don't have.

= Here's a sample implementation of a shift to the right direction:

template<class BidirIt> 
void=
 shift_rig=
ht(=
BidirIt first, BidirIt last, uns=
igned int n =3D 1) 
{ 
=C2=A0 =C2=A0 std::move_backward(f=
irst, last - n, last);<=
/span> 
}

<= /div>

This demonstrates that while std::shift is impleme= ntable with std::move/std::move_backward,

1) It isn't immedia= tely clear from the code (at least to my eyes) that this is a shift right, = unless you are intimately familiar with std::move_backward.

2) Di= fferent calls, either to std::move or to std::move_backward, are required, = depending on the shift direction.

So, implementing= std::shift would allow writing more readable code.

Thanks,

Dan

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