Add constraints to IoAwaitable

[akrzemi1]

This add constraints to IoAwaitabe, so that the concept reflects what is needed for a type to be used in Capy-coroutines:

• await_ready,
• await_resume,
• move construction.

[akrzemi1]

This addresses #356.

[cppalliance-bot]

An automated preview of the documentation is available at https://383.capy.prtest3.cppalliance.org/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-08-23 23:43:19 UTC

[cppalliance-bot]

GCOVR code coverage report https://383.capy.prtest3.cppalliance.org/gcovr/index.html
LCOV code coverage report https://383.capy.prtest3.cppalliance.org/genhtml/index.html
Coverage Diff Report https://383.capy.prtest3.cppalliance.org/diff-report/index.html

Build time: 2026-08-23 23:56:36 UTC

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.09%. Comparing base (59296c7) to head (9b957fd).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #383   +/-   ##
========================================
  Coverage    98.09%   98.09%           
========================================
  Files          130      130           
  Lines         6291     6291           
========================================
  Hits          6171     6171           
  Misses         120      120           

Flag	Coverage Δ
linux	98.08% <ø> (ø)

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Files with missing lines	Coverage Δ
include/boost/capy/task.hpp	100.00% <ø> (ø)

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[vinniefalco]

Typo in "funciton"

Should it be convertible to bool instead of same_as<bool>?

The return value excludes typed handles (e.g. std::coroutine_handle<U>). We might want a note or something.

The Doxygen comment example drops the old semantic-requirements list about stop tokens and frame allocator propagation. Consider restoring this guidance in some form.

[akrzemi1]

Typo in "funciton"

Fixed.

Should it be convertible to bool instead of same_as<bool>?

C++ awaiters are not allowed to return "convertible to bool". IoAwaitable shouldn't try to be smarter.

The return value excludes typed handles (e.g. std::coroutine_handle<U>). We might want a note or something.

My bad. I changed the concept to allow this.

The Doxygen comment example drops the old semantic-requirements list about stop tokens and frame allocator propagation. Consider restoring this guidance in some form.

They seem not to apply to the awaitable, but rather to the bodies of the resumed coroutines. Maybe instead, I will mention this in a (new) chapter which explains how to define your own coroutine?