Can the container used to create a buffer be `const`?

[0x12CC]

Specification Version

SYCL 2020 (Revision 11)

Section Number(s)

Section 4.7.2.1. Constructors, https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html#api:buffer-ctor-container.

Issue Description

This section includes the following two sentences:

1. The return type of std::data(container) is convertible to T*.
2. Data is written back to container before the completion of buffer destruction if the return type of std::data(container) is not const.

The "is not const" at the end of the second sentence is confusing. If the return type is const, this would violate constraint (1) since it wouldn't be convertible to T*. It seems the constraint should instead be that std::data(container) is convertible to const T *.

Code Example (Optional)

Relevant example is in 0x12CC/ProtoSYCL#3.

[gmlueck]

I think you're right.

FWIW, this part of the spec was reworded in #824 to use the new style. However, the previous wording had the same problem, so I think the inconsistency has been there since the first revision of SYCL 2020.

Note that there is also a comment with the same problem in the synopsis:

  /* Available only if Container is a contiguous container:
       - std::data(container) and std::size(container) are well formed
       - return type of std::data(container) is convertible to T*
     and Dimensions == 1 */

[TApplencourt]

• Thomas will try with Adative cpp and SYMSYCL to see
• Agreement on changing (1) to The return type of std::data(container) is convertible to const T*.