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Merged
merged 3 commits into from
Nov 18, 2019
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Update default-ctor proposal #104

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4f56822
Update default-ctor proposal
DuncanMcBain Oct 15, 2019
f6027be
Remove unnecessary hyphen
DuncanMcBain Oct 17, 2019
5e1db84
Slightly generalise wording around validity
DuncanMcBain Nov 18, 2019
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30 changes: 17 additions & 13 deletions default-constructed-buffers/default-constructed-buffers.md
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Expand Up @@ -7,7 +7,7 @@ Date of Creation | 2019-08-20
Target | SYCL 1.2.1
Status | _Draft_
Author | Duncan McBain [Duncan McBain](mailto:duncan@codeplay.com)
Contributors | Duncan McBain, [Gordon Brown](mailto:gordon@codeplay.com)
Contributors | Duncan McBain, [Gordon Brown](mailto:gordon@codeplay.com), [Ruyman Reyes](mailto:ruyman@codeplay.com)

## Description

Expand All @@ -34,7 +34,8 @@ aid their use in this style of generic interface.
## Proposal

The `cl::sycl::buffer` class should be augmented with an additional constructor
that takes no arguments, which initialises the buffer with a zero-size range.
that takes no arguments, which default-constructs the buffer in an
implementation-defined manner.
```c++
namespace cl {
namespace sycl {
Expand All @@ -43,7 +44,7 @@ typename AllocatorT = cl::sycl::buffer_allocator>
class buffer {
buffer();

bool is_valid() const noexcept;
bool has_storage() const noexcept;

explicit operator bool() const noexcept;
};
Expand All @@ -53,18 +54,21 @@ class buffer {
The template arguments should remain the same, so that the argument can be
rebound to a new `buffer` instance later using the copy constructor.

The `is_valid()` call would allow the programmer to query whether or not
the buffer can be used, i.e. whether or not it was constructed with a range of
size zero. The explicit conversion operator would call this same function but
allow its use in `if` statements.
The `has_storage()` call would allow the programmer to query whether or not
the buffer can be used, i.e. whether or not it was default-constructed. The
explicit conversion operator would call this same function but allow its use
in `if` statements.

Requesting access from a default-constructed buffer should throw an exception.
It is not meaningful to use a zero-sized allocation on-device. Since there is
no allocation associated with the `buffer`, `cl::sycl::buffer::set_final_data`
and `cl::sycl::buffer::set_write_back` should behave as if the `buffer` had a
final pointer of `nullptr` at all times. The other functions in the `buffer`
API should behave as though the buffer were constructed with a `range` of size
zero and otherwise behave normally.
It is not meaningful to use a default-constructed buffer. Since there
is no allocation associated with a default-constructed `buffer`,
`cl::sycl::buffer::set_final_data` and `cl::sycl::buffer::set_write_back`
should behave as if the `buffer` had a final pointer of `nullptr` at all times.
The other functions in the `buffer` API should behave as though the buffer were
constructed with a `range` of size zero and otherwise behave normally.

Explicitly constructing a buffer with a range of zero is not allowed. This does
not correspond to a valid allocation.

## Sample code

Expand Down