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be explicit in into_variant about which variant alternative is being initialized #2002

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Merged
ericniebler merged 1 commit into from
Apr 7, 2026
+24 −5
Merged

be explicit in into_variant about which variant alternative is being initialized #2002

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5 changes: 3 additions & 2 deletions include/stdexec/__detail/__into_variant.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -83,8 +83,9 @@ namespace STDEXEC
STDEXEC_TRY
{
STDEXEC::set_value(static_cast<_State&&>(__state).__rcvr_,
__variant_t{
std::tuple<_Args&&...>{static_cast<_Args&&>(__args)...}});
__variant_t{std::in_place_type<__decayed_std_tuple<_Args...>>,
std::tuple<_Args&&...>{
static_cast<_Args&&>(__args)...}});
}
STDEXEC_CATCH_ALL
{
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14 changes: 11 additions & 3 deletions include/stdexec/__detail/__when_all.hpp
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Expand Up @@ -56,6 +56,16 @@ namespace STDEXEC

struct when_all_with_variant_t
{
private:
static constexpr auto __mk_transform_fn() noexcept
{
return []<class... _Child>(__ignore, __ignore, _Child&&... __child)
{
return when_all(into_variant(static_cast<_Child&&>(__child))...);
};
}

public:
template <sender... _Senders>
constexpr auto operator()(_Senders&&... __sndrs) const -> __well_formed_sender auto
{
Expand All @@ -66,9 +76,7 @@ namespace STDEXEC
static constexpr auto transform_sender(set_value_t, _Sender&& __sndr, __ignore)
{
// transform when_all_with_variant(sndrs...) into when_all(into_variant(sndrs)...).
return __apply([&]<class... _Child>(__ignore, __ignore, _Child&&... __child)
{ return when_all(into_variant(static_cast<_Child&&>(__child))...); },
static_cast<_Sender&&>(__sndr));
return __apply(__mk_transform_fn(), static_cast<_Sender&&>(__sndr));
}
};

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10 changes: 10 additions & 0 deletions test/stdexec/algos/adaptors/test_when_all.cpp
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Expand Up @@ -15,6 +15,7 @@
*/

#include <catch2/catch.hpp>
#include <exec/any_sender_of.hpp>
#include <exec/async_scope.hpp>
#include <exec/env.hpp>
#include <exec/sender_for.hpp>
Expand Down Expand Up @@ -461,4 +462,13 @@ namespace
scope.request_stop();
ex::sync_wait(scope.on_empty());
}

TEST_CASE("regression test for #1988", "[adaptors][when_all")
{
// just test that this compiles:
using any_sender = exec::any_sender<
exec::any_receiver<ex::completion_signatures<ex::set_value_t(int), ex::set_value_t(double)>>>;
ex::sync_wait(ex::when_all_with_variant(any_sender{ex::just(1)}));
SUCCEED();
}
} // namespace
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