is_always_lockstep_sequence.h

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#pragma once
 
#include "di/execution/meta/env_of.h"
#include "di/execution/query/forwarding_query.h"
#include "di/execution/query/get_sequence_cardinality.h"
#include "di/execution/sequence/sequence_sender.h"
#include "di/function/invoke.h"
#include "di/function/tag_invoke.h"
#include "di/meta/constexpr.h"
 
namespace di::execution {
namespace is_always_lockstop_sequence_ns {
    struct Function : ForwardingQuery {
        template<typename Env>
        constexpr auto operator()(Env const& env) const {
            if constexpr (concepts::TagInvocable<Function, Env const&>) {
                static_assert(
                    concepts::ConstexprOf<meta::TagInvokeResult<Function, Env const&>, bool>,
                    "is_always_lockstep_sequence() customizations must return a di::Constexpr<bool> instance.");
                return tag_invoke(*this, env);
            } else {
                return c_<false>;
            }
        }
    };
}

constexpr inline auto is_always_lockstep_sequence = is_always_lockstop_sequence_ns::Function {};
}
 
namespace di::concepts {
template<typename Send>
concept AlwaysLockstepSequence =
    !concepts::SequenceSender<Send> || (meta::SequenceCardinality<Send> <= 1) ||
    (meta::InvokeResult<Tag<execution::is_always_lockstep_sequence>, meta::EnvOf<Send> const&>::value);
}