Add move semantics to image class

[sdebionne]

Description

Add move semantic to image.

References

• Fix part of Add move semantics support #438
• [gil] Review of move assignment operator for image class

Tasklist

• Add test case(s)
• Update doc(s)
• Ensure all CI builds pass
• Review and approve

[mloskot]

@sdebionne Thanks for the contribution. Here is my first review.

[sdebionne]

@mloskot I rebased on develop and made the changes we discussed. If the tests pass, I'll mark it ready for review.

[mloskot]

@sdebionne I also asked for feedback on the Boost list in [gil] Review of move assignment operator for image class

[mloskot]

Found a good comment related to solutions we are discussing here:

If your allocator type is stateless and/or sets is_always_equal,
then the settings of POCCA/POCMA/POCS don’t really matter
and might just as well be inconsistent.
For historical reasons, std::allocator falls into that category.

from https://quuxplusone.github.io/blog/2019/08/02/the-tough-guide-to-cpp-acronyms/#pocca-pocma-pocs

[sdebionne]

It explains why MSVC's STL has this special case for std::allocator_traits::is_always_equal and treat it as a pocma. Since we don't have it in C++11, is it OK to approximate with std::is_empty?

I'll give it a go by the end of the week.

[mloskot]

is it OK to approximate with std::is_empty?

I think, it is and http://eel.is/c++draft/allocator.traits#types-10 says

10 Type: Alloc​::​is_­always_­equal if the qualified-id Alloc​::​is_­always_­equal is valid and
denotes a type ([temp.deduct]); otherwise is_­empty<Alloc>​::​type.

Additionally, MSVC++ std lib has this base case template

template <class _Ty, class = void>
struct _Get_is_always_equal {
    using type = typename is_empty<_Ty>::type;
};

[sdebionne]

@mloskot Are you aware that "the hosted agent vs2015-win2012r2 was permanently removed on April 2nd, 2020. See https://aka.ms/blocked-hosted-agent for more information" (from azure pipelines)?

[mloskot]

@sdebionne

Are you aware that "the hosted agent vs2015-win2012r2 was permanently removed on April 2nd, 2020

Yes, I am. @sdebionne I have removed the VS2015 job now 5d531ed

BTW, I am going to use this as opportunity to switch to https://github.com/boostorg/boost-ci/ setup, but have been waiting for merge of some major refactoring of boost-ci. I will try to switch GIL AzP setup to boost-ci today/tomorrow.

[mloskot]

@sdebionne Looks good to me and ready to merge. Thanks!

Do you want to update this PR to get rid of the VS2015 job?

[mloskot]

LGTM

Thanks for the contribution!