move_into_vector.h

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// Copyright (C) 2021 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
 
#pragma once
 
#include "../../namespaces.h"
 
#include <vector>
#include <tuple>
 
namespace QDOC_CATCH_GENERATORS_UTILITIES_ABSOLUTE_NAMESPACE {
 
    namespace QDOC_CATCH_GENERATORS_TRAITS_NAMESPACE {
 
        /*!
         * Returns the type of the first element of Args.
         *
         * Args is expected to have at least one
         */
        template<typename... Args>
        using first_from_pack_t = std::tuple_element_t<0, std::tuple<Args...>>;
 
    } // end QDOC_CATCH_GENERATORS_TRAITS_NAMESPACE
 
 
    /*!
     * Builds an std::vector by moving \a movables into it.
     *
     * \a movables must be made of homogenous types.
     *
     * This function is intended to allow the construction of an
     * std::vector<T>, where T is a move only type, as an expression,
     * to lighten the idiom.
     *
     * For example, Catch's GeneratorWrapper<T> adapts a
     * std::unique_ptr, which is move only, making it impossible to
     * build a std::vector from them in place.
     *
     * Then, everywhere this is needed, a more complex approach of
     * generating the collection of objects, generating a vector of a
     * suitable size and iterating the objects to move-emplace them in
     * the vector is required.
     *
     * This not only complicates the code but is incompatible with a
     * GENERATE expression, making it extremely hard, noisy and error
     * prone to use them together.
     *
     * In those cases, then, a call to move_into_vector can be used as
     * an expression to circumvent the problem.
     */
    template<typename... MoveOnlyTypes>
    inline auto move_into_vector(MoveOnlyTypes... movables) {
        std::vector<QDOC_CATCH_GENERATORS_TRAITS_NAMESPACE::first_from_pack_t<MoveOnlyTypes...>>
            moved_into_vector;
        moved_into_vector.reserve(sizeof...(movables));
 
        (moved_into_vector.emplace_back(std::move(movables)), ...);
 
        return moved_into_vector;
    }
 
} // end QDOC_CATCH_GENERATORS_UTILITIES_ABSOLUTE_NAMESPACE