Repository navigation
[BUG]: cuda::std::span<bool> brace initialization fails with narrowing conversion error #7619
Description
Is this a duplicate?
- I confirmed there appear to be no duplicate issues for this bug and that I agree to the Code of Conduct
Type of Bug
Compile-time Error
Component
libcu++
Describe the bug
Brace initialization {} of cuda::std::span<bool> fails with narrowing conversion errors, while parentheses initialization () works. This inconsistency is due to cuda::std::span<bool> internally using __nv_bool instead of bool.
How to Reproduce
https://godbolt.org/z/h4cM67hsT
Expected behavior
cuda::std::span should build and work as std::span in the given sample code.
Reproduction link
https://godbolt.org/z/h4cM67hsT
Operating System
No response
nvidia-smi output
No response
NVCC version
No response
Metadata
Metadata
Assignees
Type
Projects
- Status
Activity
miscco commentedon Feb 10, 2026
Unfortunately, this looks like it is not an issue with our implementation, but some unfortunate interaction with the new initilizer_list constructor from C++26
If you try the same code with C++26, it will also fail to compile with the same error https://godbolt.org/z/3nn5aKEPb
The error goes away if the span is not const https://godbolt.org/z/nEc6hY5T6 or if another type other than bool is used https://godbolt.org/z/x6GK5aqeY
miscco commentedon Feb 11, 2026
Opened https://cplusplus.github.io/LWG/issue4520
bernhardmgruber commentedon Mar 25, 2026
@mhoemmen wrote a paper: http://wg21.link/P4144
mhoemmen commentedon Mar 25, 2026
@bernhardmgruber It might not be in the wg21 paper system yet. The paper has not yet been voted into the Standard (that would happen Saturday) and it WILL be revised. Please contact me offline for more details (ISO rules govern what we can say in public). (The outcome is likely good for this issue.)
bernhardmgruber commentedon Mar 25, 2026
Well, I expect it to be in the post-Croydon mailing and then the link will work. I also omitted the revision, so the link stays up to date. My intend is just to link this issue with the paper.
No need, I can lookup the minutes if I want to. I think @miscco and @griwes are following up with this issue.
miscco commentedon Mar 31, 2026
The paper has been published https://isocpp.org/files/papers/P4144R1.html
We will remove the constructor as a bugfix
mhoemmen commentedon Mar 31, 2026
The paper P4144R1 has been published, but won't be in the wg21.link system until the post-Croydon comes out in the middle of next month.