Re: [ublas] Move operators

Subject: Re: [ublas] Move operators
From: Joaquim Duran Comas (jdurancomas_at_[hidden])
Date: 2015-05-07 03:40:39

I've taken a look to g++ implementation of vector class:

The copy operator 'operator=(const vector &v)' is defined for any version
of c++ language, however the move operator 'operator=(vector &&v)' is only
defined if c++11 standard is activated.

So, for ublas we could use the c++11 based move operator if c++11 standard
is activated or use previous move operator if not. So, the code could be
something like:

class matrix {

...

matrix& operator=(const matrix& m); // always defined

#ifdef BOOST_UBLAS_CPP_GE_2011
matrix& operator=(matrix&& m);
#else
matrix& operator=(matrix& m);
#endif

....

}

Joaquim Duran

2015-04-23 23:55 GMT+02:00 Joaquim Duran Comas <jdurancomas_at_[hidden]>:

> Ok, I see. I was thinking that it was intended to be compatible with C++11.
>
> Joaquim Duran
>
>
> 2015-04-23 20:07 GMT+02:00 Nasos Iliopoulos <nasos_i_at_[hidden]>:
>
>>  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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>> Sent to: nasos_i_at_[hidden]
>>
>>
>>
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>
>