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deprecate stdexec::transform_completion_signatures[_of] #1915

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ericniebler merged 2 commits into from
Mar 6, 2026
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deprecate stdexec::transform_completion_signatures[_of] #1915

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deprecate `stdexec::transform_completion_signatures[_of]` and point f…
ericniebler Mar 5, 2026
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2 changes: 1 addition & 1 deletion examples/algorithms/retry.hpp
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Expand Up @@ -134,7 +134,7 @@ struct _retry_sender
using _value = stdexec::completion_signatures<stdexec::set_value_t(Ts...)>;

template <class Self, class... Env>
static consteval auto get_completion_signatures() -> stdexec::transform_completion_signatures<
static consteval auto get_completion_signatures() -> stdexec::__transform_completion_signatures_t<
stdexec::completion_signatures_of_t<S&, Env...>,
stdexec::completion_signatures<stdexec::set_error_t(std::exception_ptr)>,
_value,
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2 changes: 1 addition & 1 deletion examples/algorithms/then.hpp
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Expand Up @@ -70,7 +70,7 @@ struct _then_sender
stdexec::completion_signatures<stdexec::set_value_t(std::invoke_result_t<F, Args...>)>;

template <class... Env>
using _completions_t = stdexec::transform_completion_signatures<
using _completions_t = stdexec::__transform_completion_signatures_t<
stdexec::completion_signatures_of_t<S, Env...>,
stdexec::completion_signatures<stdexec::set_error_t(std::exception_ptr)>,
_set_value_t>;
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6 changes: 3 additions & 3 deletions include/exec/asio/use_sender.hpp
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Expand Up @@ -166,9 +166,9 @@ namespace experimental::execution::asio

template <typename Signatures>
using completion_signatures =
::STDEXEC::transform_completion_signatures<Signatures,
::STDEXEC::completion_signatures<>,
transform_set_value_t>;
::STDEXEC::__transform_completion_signatures_t<Signatures,
::STDEXEC::completion_signatures<>,
transform_set_value_t>;

template <typename Sender>
struct sender
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2 changes: 1 addition & 1 deletion include/exec/async_scope.hpp
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Expand Up @@ -444,7 +444,7 @@ namespace experimental::execution
using __decay_error_t = completion_signatures<set_error_t(__decay_t<_Ty>)>;

template <class _Sender, class _Env>
using __future_completions_t = transform_completion_signatures_of<
using __future_completions_t = __transform_completion_signatures_of_t<
_Sender,
__env_t<_Env>,
completion_signatures<set_stopped_t(), set_error_t(std::exception_ptr)>,
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159 changes: 133 additions & 26 deletions include/exec/completion_signatures.hpp
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Expand Up @@ -58,19 +58,25 @@ namespace experimental::execution
//! by combining explicitly provided signature types with those deduced from pointer
//! arguments.
//!
//! @tparam ExplicitSigs Explicitly specified completion signature types.
//! @tparam DeducedSigs Completion signature types to be deduced from the function arguments.
//! @param unnamed Pointer arguments (unused) used for type deduction of DeducedSigs.
//! \tparam ExplicitSigs Explicitly specified completion signature types. Must be a pack
//! of function types, the returns types of which must be one of
//! \c set_value_t, \c set_error_t, or \c set_stopped_t.
//! \tparam DeducedSigs Completion signature types to be deduced from the function
//! arguments.
//! \param unnamed Pointer arguments (unused) for type deduction of
//! \c DeducedSigs. Must be a pack of function pointer types, the
//! returns types of which must be one of \c set_value_t,
//! \c set_error_t, or \c set_stopped_t.
//!
//! @return An instance of `STDEXEC::completion_signatures` containing the combined
//! \return An instance of \c STDEXEC::completion_signatures containing the combined
//! signatures.
//!
//! @note This is a `consteval` function, meaning it is only callable in constant evaluation
//! contexts (compile-time). It always returns a default-constructed instance of the result
//! type.
//! \note This is a \c consteval function, meaning it is only callable in constant
//! evaluation contexts (compile-time). It always returns a default-constructed
//! instance of the result type.
//!
//! @note The function uses pointer arguments for type deduction without requiring actual object
//! instances.
//! \note The function uses pointer arguments for type deduction without requiring
//! actual object instances.
template <class... ExplicitSigs, class... DeducedSigs>
[[nodiscard]]
consteval auto make_completion_signatures(DeducedSigs*...) noexcept
Expand All @@ -95,33 +101,134 @@ namespace experimental::execution

//////////////////////////////////////////////////////////////////////////////////////////////////
// transform_completion_signatures

template <class _SetTag>
using keep_completion = STDEXEC::__keep_completion<_SetTag>;

using ignore_completion = STDEXEC::__ignore_completion;

template <class _SetTag, class _Fn, class... _AlgoTag>
using transform_arguments = STDEXEC::__transform_arguments<_SetTag, _Fn, _AlgoTag...>;
template <class _SetTag, template <class> class _Fn, class... _AlgoTag>
using transform_arguments =
STDEXEC::__transform_arguments<_SetTag, STDEXEC::__q1<_Fn>, _AlgoTag...>;

template <class _SetTag, class... _AlgoTag>
using decay_arguments = STDEXEC::__decay_arguments<_SetTag, _AlgoTag...>;

template <class _Completions,
class _ValueFn = keep_completion<STDEXEC::set_value_t>,
class _ErrorFn = keep_completion<STDEXEC::set_error_t>,
class _StoppedFn = keep_completion<STDEXEC::set_stopped_t>,
class _ExtraSigs = STDEXEC::completion_signatures<>>
consteval auto transform_completion_signatures(_Completions,
_ValueFn __value_fn = {},
_ErrorFn __error_fn = {},
_StoppedFn __stopped_fn = {},
_ExtraSigs = {})
//! \brief Transforms completion signatures using provided transformation functions.
//!
//! This consteval function transforms a set of completion signatures by applying
//! custom transformation functions to value, error, and stopped completion cases.
//! The result can be augmented with additional extra signatures.
//!
//! \tparam Completions The input completion signatures to transform. Must be a
//! specialization of \c STDEXEC::completion_signatures.
//! \tparam ValueFn Function object that transforms set_value_t completions.
//! Defaults to keep_completion<set_value_t>.
//! \tparam ErrorFn Function object that transforms set_error_t completions.
//! Defaults to keep_completion<set_error_t>.
//! \tparam StoppedFn Function object that transforms set_stopped_t completions.
//! Defaults to keep_completion<set_stopped_t>.
//! \tparam ExtraSigs Additional completion signatures to append to the result.
//! Must be a specialization of \c STDEXEC::completion_signatures.
//! Defaults to \c STDEXEC::completion_signatures().
//!
//! \param completions The input completion signatures object.
//! \param value_fn Value transformation function instance.
//! \param error_fn Error transformation function instance.
//! \param stopped_fn Stopped transformation function instance.
//! \param extra_sigs Extra signatures to append to the result.
//!
//! \return A transformed completion_signatures object combining the transformed
//! input signatures with the extra signatures.
//!
//! \par Example
//!
//! The following example demonstrates how to use \c transform_completion_signatures
//! to compute the completion signatures of the \c then sender.
//!
//! \code{.cpp}
//! namespace ex = STDEXEC;
//!
//! // A helper function to transform the value types of the child sender into the value
//! // types of the then sender.
//! template <class Fn, class... Args>
//! consteval auto _transform_values()
//! {
//! if constexpr (!std::invocable<Fn, Args...>)
//! {
//! // If Fn cannot be invoked with the given arguments, produce a compile-time
//! // error.
//! return exec::throw_compile_time_error<
//! WHAT(FUNCTION_IS_NOT_CALLABLE_WITH_THE_GIVEN_ARGUMENTS),
//! WHERE(IN_ALGORITHM, then_t),
//! WITH_FUNCTION(Fn),
//! WITH_ARGUMENTS(Args...)>();
//! }
//! else
//! {
//! // transform the value types of the child sender into the value types of the
//! // then sender by applying Fn to them.
//! using result_t = std::invoke_result_t<Fn, Args...>;
//! constexpr bool is_void = std::is_void_v<result_t>;
//! constexpr bool nothrow = std::is_nothrow_invocable_v<Fn, Args...>;
//! if constexpr (is_void && nothrow)
//! {
//! return ex::completion_signatures<set_value_t()>();
//! }
//! else if constexpr (is_void && !nothrow)
//! {
//! return ex::completion_signatures<set_value_t(),
//! set_error_t(std::exception_ptr)>();
//! }
//! else if constexpr (!is_void && nothrow)
//! {
//! return ex::completion_signatures<set_value_t(result_t)>();
//! }
//! else /* !is_void && !nothrow */
//! {
//! return ex::completion_signatures<set_value_t(result_t),
//! set_error_t(std::exception_ptr)>();
//! }
//! }
//! }
//!
//! template <class Child, class Fn>
//! struct then_sender
//! {
//! using sender_concept = ex::sender_t;
//!
//! template <class Self, class... Env>
//! static consteval auto get_completion_signatures()
//! {
//! // Compute the completion signatures of the child sender, and then transform
//! // them into the completion signatures of the `then` sender.
//! auto child_completions = exec::get_child_completion_signatures<Self, Child, Env...>();
//! auto value_fn = []<class... Args>() { return _transform_values<Fn, Args...>(); };
//!
//! return exec::transform_completion_signatures(child_completions, value_fn);
//! }
//!
//! // ...
//! };
//! \endcode
//!
//! \note This function is evaluated at compile-time (consteval).
template <class Completions,
class ValueFn = keep_completion<STDEXEC::set_value_t>,
class ErrorFn = keep_completion<STDEXEC::set_error_t>,
class StoppedFn = keep_completion<STDEXEC::set_stopped_t>,
class ExtraSigs = STDEXEC::completion_signatures<>>
consteval auto transform_completion_signatures(Completions,
ValueFn value_fn = {},
ErrorFn error_fn = {},
StoppedFn stopped_fn = {},
ExtraSigs = {})
{
return STDEXEC::__transform_completion_signatures(_Completions{},
__value_fn,
__error_fn,
__stopped_fn,
_ExtraSigs{});
return STDEXEC::__transform_completion_signatures(Completions{},
value_fn,
error_fn,
stopped_fn,
ExtraSigs{});
}
} // namespace experimental::execution

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20 changes: 10 additions & 10 deletions include/exec/detail/shared.hpp
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Expand Up @@ -133,13 +133,13 @@ namespace experimental::execution::__shared
////////////////////////////////////////////////////////////////////////////////////////
template <class _CvSender, class _Env>
using __result_variant_t =
__transform_completion_signatures_t<__completion_signatures_of_t<_CvSender, _Env>,
__mbind_front_q<__decayed_tuple, set_value_t>::__f,
__mbind_front_q<__decayed_tuple, set_error_t>::__f,
__tuple<set_stopped_t>,
__munique<__qq<__variant>>::__f,
__tuple<set_error_t, std::exception_ptr>,
__tuple<set_stopped_t>>;
__transform_reduce_completion_signatures_t<__completion_signatures_of_t<_CvSender, _Env>,
__mbind_front_q<__decayed_tuple, set_value_t>::__f,
__mbind_front_q<__decayed_tuple, set_error_t>::__f,
__tuple<set_stopped_t>,
__munique<__qq<__variant>>::__f,
__tuple<set_error_t, std::exception_ptr>,
__tuple<set_stopped_t>>;

////////////////////////////////////////////////////////////////////////////////////////
template <class _CvChild, class _Env>
Expand Down Expand Up @@ -461,12 +461,12 @@ namespace experimental::execution::__shared
};

template <class _Cv, class _CvSender, class _Env>
using __make_completions_t = __try_make_completion_signatures<
using __make_completions_t = __transform_completion_signatures_of_t<
_CvSender,
__env_t<_Env>,
completion_signatures<set_error_t(__mcall1<_Cv, std::exception_ptr>), set_stopped_t()>,
__mtransform<_Cv, __mcompose<__qq<completion_signatures>, __qf<set_value_t>>>,
__mtransform<_Cv, __mcompose<__qq<completion_signatures>, __qf<set_error_t>>>>;
__mtransform<_Cv, __mcompose<__qq<completion_signatures>, __qf<set_value_t>>>::template __f,
__mtransform<_Cv, __mcompose<__qq<completion_signatures>, __qf<set_error_t>>>::template __f>;

// split completes with const T&. ensure_started completes with T&&.
template <class _Tag>
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2 changes: 1 addition & 1 deletion include/exec/into_tuple.hpp
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Expand Up @@ -53,7 +53,7 @@ namespace experimental::execution
STDEXEC::completion_signatures<set_error_t(std::exception_ptr), set_value_t(_Tuple)>;

template <class _Sender, class... _Env>
using __completions_t = transform_completion_signatures<
using __completions_t = __transform_completion_signatures_t<
__completion_signatures_of_t<_Sender, _Env...>,
__minvoke_q<__tuple_completions_t, __result_tuple_t<_Sender, _Env...>>,
__mconst<STDEXEC::completion_signatures<>>::__f>;
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2 changes: 1 addition & 1 deletion include/exec/just_from.hpp
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Expand Up @@ -115,7 +115,7 @@ namespace experimental::execution
{
template <class Fn>
using __f = STDEXEC::__concat_completion_signatures_t<STDEXEC::__call_result_t<Fn, _probe_fn>,
STDEXEC::__eptr_completion>;
STDEXEC::__eptr_completion_t>;
};

template <class Fn>
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4 changes: 2 additions & 2 deletions include/exec/libdispatch_queue.hpp
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Expand Up @@ -258,14 +258,14 @@ namespace experimental::execution
STDEXEC::__mbind_front_q<bulk_non_throwing_t, Fun, Shape>,
STDEXEC::__q<STDEXEC::__mand>>::value,
STDEXEC::completion_signatures<>,
STDEXEC::__eptr_completion>;
STDEXEC::__eptr_completion_t>;

template <class... Tys>
using set_value_t =
STDEXEC::completion_signatures<STDEXEC::set_value_t(STDEXEC::__decay_t<Tys>...)>;

template <class Self, class... Env>
using _completions_t = STDEXEC::transform_completion_signatures<
using _completions_t = STDEXEC::__transform_completion_signatures_t<
STDEXEC::__completion_signatures_of_t<STDEXEC::__copy_cvref_t<Self, Sender>, Env...>,
with_error_invoke_t<STDEXEC::__copy_cvref_t<Self, Sender>, Env...>,
set_value_t>;
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4 changes: 2 additions & 2 deletions include/exec/materialize.hpp
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Expand Up @@ -95,7 +95,7 @@ namespace experimental::execution
using __materialize_error = completion_signatures<set_value_t(set_error_t, _Err)>;

template <class _Self, class... _Env>
using __completions_t = __transform_completion_signatures_t<
using __completions_t = __transform_reduce_completion_signatures_t<
__completion_signatures_of_t<__copy_cvref_t<_Self, _Sender>, _Env...>,
__materialize_value,
__materialize_error,
Expand Down Expand Up @@ -202,7 +202,7 @@ namespace experimental::execution
using __dematerialize_value = completion_signatures<__decay_t<_Tag>(_Args...)>;

template <class _Self, class... _Env>
using __completions_t = transform_completion_signatures<
using __completions_t = __transform_completion_signatures_t<
__completion_signatures_of_t<__copy_cvref_t<_Self, _Sender>, _Env...>,
completion_signatures<>,
__mtry_q<__dematerialize_value>::template __f>;
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8 changes: 4 additions & 4 deletions include/exec/repeat_n.hpp
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Expand Up @@ -197,15 +197,15 @@ namespace experimental::execution
using __error_t = completion_signatures<set_error_t(__decay_t<_Error>)>;

template <typename _Sender, typename... _Env>
using __with_eptr_completion_t = __eptr_completion_unless<
using __with_eptr_completion_t = __eptr_completion_unless_t<__mbool<
__cmplsigs::__partitions_of_t<
__completion_signatures_of_t<_Sender, _Env...>>::__nothrow_decay_copyable::__errors::value
&& (__nothrow_connectable<_Sender, __receiver_archetype<_Env>> && ...)>;
&& (__nothrow_connectable<_Sender, __receiver_archetype<_Env>> && ...)>>;

template <class _Child, class... _Env>
using __completions_t = STDEXEC::transform_completion_signatures<
using __completions_t = STDEXEC::__transform_completion_signatures_t<
__completion_signatures_of_t<_Child &, _Env...>,
STDEXEC::transform_completion_signatures<
STDEXEC::__transform_completion_signatures_t<
__completion_signatures_of_t<STDEXEC::schedule_result_t<trampoline_scheduler>, _Env...>,
__with_eptr_completion_t<_Child, _Env...>,
__cmplsigs::__default_set_value,
Expand Down
6 changes: 3 additions & 3 deletions include/exec/repeat_until.hpp
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Expand Up @@ -283,9 +283,9 @@ namespace experimental::execution
}
else
{
constexpr bool __has_nothrow_connect =
(__nothrow_connectable<__child_t, __receiver_archetype<_Env>> || ...);
constexpr auto __eptr_sigs = __eptr_completion_unless<__has_nothrow_connect>();
using __has_nothrow_connect_t =
__mbool<(__nothrow_connectable<__child_t, __receiver_archetype<_Env>> || ...)>;
constexpr auto __eptr_sigs = __eptr_completion_unless_t<__has_nothrow_connect_t>();
constexpr auto __bouncer_sigs = exec::transform_completion_signatures(
get_completion_signatures<__bouncer_t, _Env...>(),
exec::ignore_completion()); // drop the set_value_t() completion from the
Expand Down
8 changes: 4 additions & 4 deletions include/exec/sequence.hpp
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Expand Up @@ -258,9 +258,9 @@ namespace experimental::execution
}
else
{
using __env_t = STDEXEC::__mfront<Env..., STDEXEC::env<>>;
using __rcvr_t = STDEXEC::__receiver_archetype<__env_t>;
constexpr bool nothrow = (STDEXEC::__nothrow_connectable<Senders, __rcvr_t> && ...);
using __env_t = STDEXEC::__mfront<Env..., STDEXEC::env<>>;
using __rcvr_t = STDEXEC::__receiver_archetype<__env_t>;
constexpr bool __is_nothrow = (STDEXEC::__nothrow_connectable<Senders, __rcvr_t> && ...);

// The completions of the sequence sender are the error and stopped completions of all the
// child senders plus the value completions of the last child sender.
Expand All @@ -272,7 +272,7 @@ namespace experimental::execution
STDEXEC::get_completion_signatures<Senders, Env...>(),
exec::ignore_completion())...,
STDEXEC::get_completion_signatures<STDEXEC::__mback<Senders...>, Env...>(),
STDEXEC::__eptr_completion_unless<nothrow>());
STDEXEC::__eptr_completion_unless_t<STDEXEC::__mbool<__is_nothrow>>());
}
}

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2 changes: 1 addition & 1 deletion include/exec/sequence/ignore_all_values.hpp
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Expand Up @@ -249,7 +249,7 @@ namespace experimental::execution
};

template <class _Sigs>
using __result_variant_ = __transform_completion_signatures_t<
using __result_variant_ = __transform_reduce_completion_signatures_t<
_Sigs,
__mconst<__mlist<>>::__f,
__mcompose_q<__mlist, __mbind_front_q<__decayed_tuple, set_error_t>::__f>::__f,
Expand Down
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