Yes, this has been asked before, and the answer has been:
valarray
s (value arrays) are intended to bring some of the speed of Fortran to C++. You wouldn't make avalarray
of pointers so the compiler can make assumptions about the code and optimise it better. (The main reason that Fortran is so fast is that there is no pointer type so there can be no pointer aliasing.)
or:
valarray
is also supposed to eliminate any possibility of aliasing [...]
But these answers make no sense to me.
valarray
and vector
are class templates, and as such, they don't even exist until instantiated.
And of course, a vector<int>
doesn't cause aliasing issues any more than valarray<int>
does.
Given this, what was the purpose of valarray
, and why did they not simply put the same functionality into vector
instead?
Separation of concern? A vector
and a valarray
solve different problems. Quoting from the standard, a vector
is a (§23.3.6.1 [vector.overview] p1
)
... sequence container that supports random access iterators. In addition, it supports (amortized) constant time insert and erase operations at the end; insert and erase in the middle take linear time. Storage management is handled automatically, though hints can be given to improve efficiency.
while a valarray
is a (§26.6.2.1 [template.valarray.overview] p1
)
... one-dimensional smart array, with elements numbered sequentially from zero. It is a representation of the mathematical concept of an ordered set of values. The illusion of higher dimensionality may be produced by the familiar idiom of computed indices, together with the powerful subsetting capabilities provided by the generalized subscript operators.
As you can see, they serve different purposes. A vector
is a generalized dynamic array, while a valarray
represents a set of values. It's also not resizeable and only assignable.
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