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adds assert_with concept and uses it for get_completion_signatures an… #1815

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adds assert_with concept and uses it for get_completion_signatures an… #1815

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5 changes: 4 additions & 1 deletion include/stdexec/__detail/__connect.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@
#pragma once

#include "__execution_fwd.hpp"
#include "__diagnostics.hpp"

// include these after __execution_fwd.hpp
#include "__completion_signatures_of.hpp"
Expand Down Expand Up @@ -206,7 +207,9 @@ namespace STDEXEC {
class _Receiver,
class _DeclFn = __connect_declfn_t<_Sender, _Receiver>
>
requires __connectable_to<_Sender, _Receiver>
requires assert_with<
__connectable_to<_Sender, _Receiver>,
__connect_error_t<transform_sender_result_t<_Sender, env_of_t<_Receiver>>, _Receiver>>
STDEXEC_ATTRIBUTE(always_inline)
constexpr auto operator()(_Sender&& __sndr, _Receiver&& __rcvr) const
noexcept(__nothrow_callable<_DeclFn>) -> __call_result_t<_DeclFn> {
Expand Down
28 changes: 28 additions & 0 deletions include/stdexec/__detail/__diagnostics.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -115,6 +115,18 @@ namespace STDEXEC {
_WITH_ENVIRONMENT_(_Env)...
>;

struct _CONNECT_ERROR_ {};
struct _UNABLE_TO_CONNECT_THE_SENDER_TO_THE_RECEIVER_ { };

template <class _Sender, class _Receiver>
using __connect_error_t = __mexception<
_WHAT_(_CONNECT_ERROR_),
_WHY_(_UNABLE_TO_CONNECT_THE_SENDER_TO_THE_RECEIVER_),
_WITH_PRETTY_SENDER_<_Sender>,
_WITH_RECEIVER_(_Receiver),
_WITH_ENVIRONMENT_(env_of_t<_Receiver>)
>;

#if __cpp_lib_constexpr_exceptions >= 2025'02L // constexpr exception types, https://wg21.link/p3378

using __exception = ::std::exception;
Expand Down Expand Up @@ -258,6 +270,22 @@ namespace STDEXEC {

constexpr bool operator==(const __not_a_scheduler&) const noexcept = default;
};

template<bool _MustBeTrue, class _WithError>
struct __assert_with;

template<class _WithError>
struct __assert_with<false, _WithError> {
static constexpr bool value = __ok<_WithError>;
static_assert(__ok<_WithError>, "concept assertion failed with..");
};
template<class _Elide>
struct __assert_with<true, _Elide> {
static constexpr bool value = true;
};

template<bool _MustBeTrue, class _WithError>
concept assert_with = __assert_with<_MustBeTrue, _WithError>::value;
} // namespace STDEXEC

////////////////////////////////////////////////////////////////////////////////
Expand Down
9 changes: 6 additions & 3 deletions include/stdexec/__detail/__get_completion_signatures.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -238,10 +238,11 @@ namespace STDEXEC {
}

template <class _Sender, class _Env>
requires __has_get_completion_signatures<_Sender, _Env>
requires assert_with<
__has_get_completion_signatures<_Sender, _Env>,
__unrecognized_sender_error_t<transform_sender_result_t<_Sender, _Env>, _Env>>
consteval auto get_completion_signatures() {
using __new_sndr_t = transform_sender_result_t<_Sender, _Env>;
static_assert(!__merror<__new_sndr_t>);
return __cmplsigs::__get_completion_signatures_helper<__new_sndr_t, _Env>();
}

Expand All @@ -255,7 +256,9 @@ namespace STDEXEC {
///////////////////////////////////////////////////////////////////////////////////////////////////
// An minimally constrained alias for the result of get_completion_signatures:
template <class _Sender, class... _Env>
requires enable_sender<__decay_t<_Sender>>
requires assert_with<
enable_sender<__decay_t<_Sender>>,
__unrecognized_sender_error_t<__decay_t<_Sender>, _Env...>>
using __completion_signatures_of_t =
decltype(STDEXEC::get_completion_signatures<_Sender, _Env...>());

Expand Down
4 changes: 1 addition & 3 deletions test/stdexec/concepts/test_concepts_sender.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -93,7 +93,7 @@ namespace {
ex::set_stopped_t()
>;

auto connect(empty_recv::recv0&&) const -> oper {
auto connect(empty_recv::recv0&&) const -> oper {
return {};
}
};
Expand Down Expand Up @@ -171,11 +171,9 @@ namespace {
"not all combinations of senders & receivers satisfy the sender_to concept",
"[concepts][sender]") {
REQUIRE_FALSE(ex::sender_to<my_sender0, empty_recv::recv_int>);
REQUIRE_FALSE(ex::sender_to<my_sender0, empty_recv::recv0_ec>);
REQUIRE_FALSE(ex::sender_to<my_sender0, empty_recv::recv_int_ec>);
REQUIRE_FALSE(ex::sender_to<my_sender_int, empty_recv::recv0>);
REQUIRE_FALSE(ex::sender_to<my_sender_int, empty_recv::recv0_ec>);
REQUIRE_FALSE(ex::sender_to<my_sender_int, empty_recv::recv_int_ec>);
}

TEST_CASE(
Expand Down