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### 618. valarray::cshift() effects on empty array

Section: 26.7.2.8 [valarray.members] Status: CD1 Submitter: Gabriel Dos Reis Opened: 2007-01-10 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

I would respectfully request an issue be opened with the intention to clarify the wording for `size() == 0` for `cshift`.

Proposed resolution:

Change 26.7.2.8 [valarray.members], paragraph 10:

>     valarray<T> cshift(int n) const;

> > This function returns an object of class `valarray<T>`, of length `size()`, each of whose elements `I` is `(*this)[(I + n ) % size()]`. Thus, if element zero is taken as the leftmost element, a positive value of n shifts the elements circularly left n places. that is a circular shift of `*this`. If element zero is taken as the leftmost element, a non-negative value of n shifts the elements circularly left n places and a negative value of n shifts the elements circularly right -n places.

Rationale:

We do not believe that there is any real ambiguity about what happens when `size() == 0`, but we do believe that spelling this out as a C++ expression causes more trouble that it solves. The expression is certainly wrong when `n < 0`, since the sign of % with negative arguments is implementation defined.

[ Kona (2007) Changed proposed wording, added rationale and set to Review. ]