- shared_ptr array range loop doesn't work - 4 Updates
- Vector Fractal Bloom... - 1 Update
| Pavel <pauldontspamtolk@removeyourself.dontspam.yahoo>: May 19 11:19PM -0400 > Is there a way to get range loops to work with arrays stored in > shared pointers? These shared pointers do not store arrays. They store pointers to memory object allocated with operator new[]. In other words, the type shared_ptr<mystruct[3]>::element_type is same as shared_ptr<mystruct>::element_type i.e. mystruct. To get a feeling of why it's natural, note that the type of the expression "new mystruct[3]" that you use to initalize sp is mystruct*, not mystruct (*)[3]. Therefore, it is not possible to iterate the way you want: there is no either constexpr 3 anywhere in the type of shared_ptr<mystruct[3]> or non-constexpr 3 that could be extracted from the object in memory in any implementation-independent way. Thus, there is no way for C++ compiler to generate the code that would compute the end of the range. > return 0; > } > I've tried other combinations too, nothing works. HTH -Pavel |
| Muttley@dastardlyhq.com: May 20 08:58AM On Fri, 19 May 2023 23:19:30 -0400 >To get a feeling of why it's natural, note that the type of the >expression "new mystruct[3]" that you use to initalize sp is mystruct*, >not mystruct (*)[3]. Fair enough. Does make me wonder why they bothered to introduce this particular semantic for shared pointers. |
| "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>: May 20 02:39PM -0700 On 5/20/2023 2:38 PM, Alf P. Steinbach wrote: > `shared_ptr` currently makes available an indexing operator if the item > type is array: <url: > https://en.cppreference.com/w/cpp/memory/shared_ptr/operator_at>. Thanks! I did not know that. |
| "Alf P. Steinbach" <alf.p.steinbach@gmail.com>: May 20 11:38PM +0200 On 2023-05-20 5:19 AM, Pavel wrote: > non-constexpr 3 that could be extracted from the object in memory in any > implementation-independent way. Thus, there is no way for C++ compiler > to generate the code that would compute the end of the range. Oh, there is such a way. `shared_ptr` currently makes available an indexing operator if the item type is array: <url: https://en.cppreference.com/w/cpp/memory/shared_ptr/operator_at>. It could just as easily make available `begin` and `end` operations for array item type, and then a range based loop would Just Work. My earlier answer in this thread showed how to do that oneself. And what I can do (it was trivial enough that a dino could manage) the committee could do. - Alf |
| "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>: May 20 01:21PM -0700 On 5/12/2022 12:16 PM, Chris M. Thomasson wrote: > Using my experimental vector field to generate a fractal formation. Here > is generation two: > https://fractalforums.org/gallery/1612-120522191048.png Gate to another world. An adventure in equipotentials... ;^) https://i.ibb.co/w79XDxJ/Gates-to-Another-World.png |
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