Can I use rvalue to store the intermediate results

Asked Apr 12 '16 at 10:00

Active Apr 12 '16 at 10:00

Viewed 75 times

I found it slow when calculate expression of array. So I wonder about can I use rvalue to store the intermediate results for reducing alloc action?

#include "SArray.hpp"

template <typename T>
SArray<T>&& operator* (SArray<T>&& s, const T& scale) {
    for (size_t i = 0; i < s.size(); ++i)
        s[i] *= scale;
    return std::move(s);
}

int main() {

    SArray<int> w = SArray<int>({1,2,3,4,5,6}) * 2;

    return 0;
}

asked Apr 12 '16 at 10:00

Luster

Yes. You can. Topic close :P – Nawaz Apr 12 '16 at 10:06
1

BTW, you should write `return s;`.. that is better than `return std::move(s);` The former facilitates copy/move-elision by the compiler. – Nawaz Apr 12 '16 at 10:08
Also, if `SArray` stores the data as part of the object (rather than holding a pointer or something), then moves will likely be as slow as copies. – TartanLlama Apr 12 '16 at 10:10
Is [this](http://www.java2s.com/Tutorial/Cpp/0040__Data-Types/SArray.htm) your `SArray`? – Yakk - Adam Nevraumont Apr 12 '16 at 12:48
@Nawaz `std::move` is a no-op in this case. The function returns a reference (to the same object that `s` refers to) - there is no copy or move to elide. – Igor Tandetnik Apr 12 '16 at 13:28
@IgorTandetnik: ahh.. yes. I didn't notice that ...(But then I guess that is *not* what OP intended). – Nawaz Apr 12 '16 at 13:55
@Yakk Yep I come this idea when learning ETs – Luster Apr 13 '16 at 04:15
1

Dont think that SArray class implements move, you should add move assignment operator to the class. – thorsan Apr 13 '16 at 05:55

Can I use rvalue to store the intermediate results

0 Answers0