Re: [ublas] Move operators

Subject: Re: [ublas] Move operators
From: Nasos Iliopoulos (nasos_i_at_[hidden])
Date: 2015-04-23 14:07:23

Joaquim,
the move semantics in uBlas were implemented before the C++11 standard 
was adopted. We will need update the implementation to reflect the C++11 
changes with respect to move constructors. I would say that gcc's vector 
implementation of the C++11 constructors design is a good reference 
implementation.

Best,
Nasos

On 04/21/2015 07:13 PM, Joaquim Duran Comas wrote:
> Hello all,
>
> I've some questions regarding to move operators:
>
> 1 - As Houndie, in request #20 in boost/org/ublas, I would like to 
> include the rreference operator (&&) before the matrix parameter:
>
> -        fixed_matrix &operator = (fixed_matrix m) {
> +        fixed_matrix &operator = (fixed_matrix && m) {
>
> This is how I've seen defined the move operator in may places. 
> However, the comment tells that the parameter is passed by value to 
> enable the move semantics. I've searched about move operator with 
> parameter by value. I've found this article 
> http://cpptruths.blogspot.com.es/2012/03/rvalue-references-in-constructor-when.html.
>
> The article tells that to activate the move semantics, the parameter 
> should be passed by value (as you tell), but it is not applied the the 
> move constructor or move iterator:
>
> |class| |Book {|
> |public||:|
> |||Book(std::string title,|
> |||std::vector<std::string> authors, // <-- Parameter by value|
> |||size_t| |pub_day|
> |||std::string pub_month,|
> |||size_t| |pub_year)|
> |||: _title    (std::move(title)),|
> |||_authors (std::move(authors)), // <-- The parameter is moved to 
> member variable|
> |||_pub_day (pub_day),|
> |||_pub_month(std::move(pub_month)),|
> |||_pub_year (pub_year)|
> |||{}|
> |||// ....|
> |||// ....|
> |};|
>
> 2 - AFAIK, with the implementation of move semantics has not 
> deprecated the copy semantics. As it is defined in the source code, it 
> looks like that move semantic could not be used with copy semantics. 
> Both semantics should be used at the same time in a C++11 compiler:
>
> // Copy semantics
> matrix m1;
> matrix m2(m1);
> m2 = m1;
>
> // Move semantics
> matrix m1;
> matrix m2(std::move(m1));
> m3 = std::move(m2);
>
> Please, could you confirm that move operators are defined as expected?
>
> Thanks and Best Regards,
> Joaquim Duran
>
>
>
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