video-pc/utils/builderutils.h

// Copyright (C) 2020 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0

#pragma once

#include <functional>
#include <tuple>

// C++14 compatible apply implementation
namespace detail {
    template<class F, class Tuple, std::size_t... I>
    constexpr auto apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>)
        -> decltype(std::forward<F>(f)(std::get<I>(std::forward<Tuple>(t))...))
    {
        return std::forward<F>(f)(std::get<I>(std::forward<Tuple>(t))...);
    }
}

template<class F, class Tuple>
constexpr auto apply(F&& f, Tuple&& t)
    -> decltype(detail::apply_impl(std::forward<F>(f), std::forward<Tuple>(t),
                                   std::make_index_sequence<std::tuple_size<std::decay_t<Tuple>>::value>{}))
{
    return detail::apply_impl(std::forward<F>(f), std::forward<Tuple>(t),
                              std::make_index_sequence<std::tuple_size<std::decay_t<Tuple>>::value>{});
}

namespace Building {

class NestId {};

template <typename Id, typename Arg>
class IdAndArg
{
public:
    IdAndArg(Id, const Arg &arg) : arg(arg) {}
    const Arg arg; // FIXME: Could be const &, but this would currently break bindTo().
};

// The main dispatcher

template<typename X, typename Id, typename P>
void doit(X x, Id id, P p);

template <typename X> class BuilderItem
{
public:
    // Property setter
    template <typename Id, typename Arg>
    BuilderItem(IdAndArg<Id, Arg> && idarg)
        : apply([&idarg](X *x) { doit(x, Id{}, idarg.arg); })
    {}

    // Nested child object
    template <typename Inner>
    BuilderItem(Inner && p)
        : apply([&p](X *x) { doit(x, NestId{}, std::forward<Inner>(p)); })
    {}

    const std::function<void(X *)> apply;
};

#define QTC_DEFINE_BUILDER_SETTER(name, setter) \
class name##_TAG {}; \
template <typename ...Args> \
inline auto name(Args &&...args) { \
    return Building::IdAndArg{name##_TAG{}, std::tuple<Args...>{std::forward<Args>(args)...}}; \
} \
template <typename L, typename ...Args> \
inline void doit(L *x, name##_TAG, const std::tuple<Args...> &arg) { \
    apply(&L::setter, std::tuple_cat(std::make_tuple(x), arg)); \
}

} // Building