gather_signatures.h

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#pragma once
 
#include "di/execution/concepts/completion_signature.h"
#include "di/execution/concepts/sender_in.h"
#include "di/execution/meta/completion_signatures_of.h"
#include "di/meta/algorithm.h"
#include "di/meta/core.h"
#include "di/meta/language.h"
#include "di/meta/util.h"
 
namespace di::meta {
namespace detail {
    template<bool>
    struct IndirectMetaApply {
        template<template<typename...> typename T, typename... Args>
        using MetaApply = T<Args...>;
    };
 
    template<template<typename...> typename F, typename List>
    struct MetaApply;
 
    template<template<typename...> typename F, typename... Args>
    struct MetaApply<F, meta::List<Args...>>
        : TypeConstant<typename IndirectMetaApply<concepts::AlwaysTrue<Args...>>::template MetaApply<F, Args...>> {};
 
    template<typename Tag, typename Completions, template<typename...> typename Tup>
    struct GatherSignaturesHelper;
 
    template<typename Tag, template<typename...> typename Tup>
    struct GatherSignaturesHelper<Tag, List<>, Tup> : TypeConstant<List<>> {};
 
    template<typename Tag, typename T, typename... Rest, template<typename...> typename Tup>
    struct GatherSignaturesHelper<Tag, List<T, Rest...>, Tup> : GatherSignaturesHelper<Tag, List<Rest...>, Tup> {};
 
    template<typename Tag, concepts::CompletionSignature T, typename... Rest, template<typename...> typename Tup>
    requires(concepts::SameAs<meta::LanguageFunctionReturn<T>, Tag>)
    struct GatherSignaturesHelper<Tag, List<T, Rest...>, Tup>
        : TypeConstant<PushFront<Type<GatherSignaturesHelper<Tag, List<Rest...>, Tup>>,
                                 meta::Type<MetaApply<Tup, meta::AsList<T>>>>> {};
}
 
template<typename Tag, typename S, typename E, template<typename...> typename Tuple,
         template<typename...> typename Variant>
requires(concepts::SenderIn<S, E>)
using GatherSignatures = meta::Type<detail::MetaApply<
    Variant, meta::Type<detail::GatherSignaturesHelper<Tag, meta::AsList<meta::CompletionSignaturesOf<S, E>>, Tuple>>>>;
}