get_sequence_cardinality.h

Go to the documentation of this file.

#pragma once
 
#include "di/execution/meta/env_of.h"
#include "di/execution/query/forwarding_query.h"
#include "di/execution/sequence/sequence_sender.h"
#include "di/function/invoke.h"
#include "di/function/tag_invoke.h"
#include "di/math/numeric_limits.h"
#include "di/meta/constexpr.h"
#include "di/types/integers.h"
 
namespace di::execution {
namespace get_sequence_cardinality_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&>, usize>,
                              "sequence_cardinality() customizations must return a di::Constexpr<usize> instance.");
                return tag_invoke(*this, env);
            } else {
                return c_<math::NumericLimits<usize>::max>;
            }
        }
    };
}

constexpr inline auto get_sequence_cardinality = get_sequence_cardinality_ns::Function {};
}
 
namespace di::meta {
template<typename Sequence>
constexpr inline auto SequenceCardinality =
    !concepts::SequenceSender<Sequence>
        ? 1ZU
        : meta::InvokeResult<decltype(execution::get_sequence_cardinality), meta::EnvOf<Sequence>>::value;
}