any_movable.hpp

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#pragma once
 
/// @file userver/utils/any_movable.hpp
/// @brief @copybrief utils::AnyMovable
 
#include <any>  // for std::bad_any_cast
#include <initializer_list>
#include <memory>
#include <type_traits>
#include <utility>
 
USERVER_NAMESPACE_BEGIN
 
/// Utilities
namespace utils {
 
/// @ingroup userver_universal userver_containers
///
/// @brief Replacement for `std::any` that is not copyable. It allows to store
/// non-copyable and even non-movable types.
///
/// Usage example:
/// @snippet universal/src/utils/any_movable_test.cpp  AnyMovable example usage
class AnyMovable final {
public:
    /// Creates an empty `AnyMovable`
    constexpr AnyMovable() noexcept = default;
 
    /// `AnyMovable` is movable, but not copyable
    AnyMovable(AnyMovable&&) noexcept = default;
    AnyMovable& operator=(AnyMovable&&) noexcept = default;
 
    /// Copies or moves the provided object inside the `AnyMovable`. `const`,
    /// reference, arrays and function pointers are decayed.
    template <typename ValueType, typename = std::enable_if_t<!std::is_same_v<AnyMovable, std::decay_t<ValueType>>>>
    /*implicit*/ AnyMovable(ValueType&& value);
 
    /// In-place constructs an object of the specified type
    template <typename ValueType, typename... Args>
    explicit AnyMovable(std::in_place_type_t<ValueType> tag, Args&&... args);
 
    /// In-place constructs an object of the specified type
    template <typename ValueType, typename Item, typename... Args>
    explicit AnyMovable(std::in_place_type_t<ValueType> tag, std::initializer_list<Item> list, Args&&... args);
 
    /// Copies or moves the provided object inside the `AnyMovable`. `const`,
    /// reference, arrays and function pointers are decayed.
    template <typename ValueType>
    AnyMovable& operator=(ValueType&& rhs);
 
    /// Check if the `AnyMovable` is empty
    bool HasValue() const noexcept;
 
    /// Destroy the old contents, making `*this` empty
    void Reset() noexcept;
 
    /// In-place constructs an object of the specified type
    template <typename ValueType, typename... Args>
    ValueType& Emplace(Args&&... args);
 
    /// In-place constructs an object of the specified type
    template <typename ValueType, typename Item, typename... Args>
    ValueType& Emplace(std::initializer_list<Item> list, Args&&... args);
 
private:
    struct HolderBase;
 
    template <typename ValueType>
    struct Holder;
 
    struct HolderDeleter {
        void operator()(HolderBase* holder) noexcept;
    };
 
    template <typename ValueType>
    friend ValueType* AnyCast(AnyMovable*) noexcept;
 
    template <typename ValueType>
    friend const ValueType* AnyCast(const AnyMovable*) noexcept;
 
    std::unique_ptr<HolderBase, HolderDeleter> content_;
};
 
/// @brief The exception that is thrown when `AnyCast` fails
class BadAnyMovableCast final : public std::bad_any_cast {
public:
    const char* what() const noexcept override;
};
 
/// @return nullptr if operand is nullptr or type of the data stored in operand
/// does not match ValueType
template <typename ValueType>
ValueType* AnyCast(AnyMovable* operand) noexcept;
 
/// @return nullptr if operand is nullptr or type of the data stored in operand
/// does not match ValueType
template <typename ValueType>
const ValueType* AnyCast(const AnyMovable* operand) noexcept;
 
/// @note Cast to a reference type to avoid extra copies
/// @throw BadAnyMovableCast if type of the data stored in operand
/// does not match ValueType
template <typename ValueType>
ValueType AnyCast(AnyMovable& operand);
 
/// @note Cast to a reference type to avoid extra copies
/// @throw BadAnyMovableCast if type of the data stored in operand
/// does not match ValueType
template <typename ValueType>
ValueType AnyCast(const AnyMovable& operand);
 
/// @note Cast to a reference type to avoid extra moves
/// @throw BadAnyMovableCast if type of the data stored in operand
/// does not match ValueType
template <typename ValueType>
ValueType AnyCast(AnyMovable&& operand);
 
struct AnyMovable::HolderBase {
    using DeleterType = void (*)(HolderBase&) noexcept;
 
    DeleterType deleter;
};
 
template <typename ValueType>
struct AnyMovable::Holder final : public HolderBase {
    static_assert(
        std::is_same_v<ValueType, std::decay_t<ValueType>>,
        "The requested type can't be stored in an AnyMovable"
    );
 
    ValueType held;
 
    static void Deleter(HolderBase& holder) noexcept { delete &static_cast<Holder&>(holder); }
 
    template <typename... Args>
    static std::unique_ptr<HolderBase, HolderDeleter> Make(Args&&... args) {
        return std::unique_ptr<HolderBase, HolderDeleter>{
            // intended raw ctor call, sometimes casts
            // NOLINTNEXTLINE(google-readability-casting)
            new Holder{{&Deleter}, ValueType(std::forward<Args>(args)...)}};
    }
 
    static ValueType* GetIf(const AnyMovable* any) noexcept {
        return (any && any->content_ && any->content_->deleter == &Deleter) ? &static_cast<Holder&>(*any->content_).held
                                                                            : nullptr;
    }
};
 
template <typename ValueType, typename>
AnyMovable::AnyMovable(ValueType&& value)
    : content_(Holder<std::decay_t<ValueType>>::Make(std::forward<ValueType>(value))) {
    static_assert(
        !std::is_same_v<AnyMovable*, std::decay_t<ValueType>> &&
            !std::is_same_v<const AnyMovable*, std::decay_t<ValueType>>,
        "AnyMovable misuse detected: trying to wrap AnyMovable* in another "
        "AnyMovable. The pointer was probably meant to be dereferenced."
    );
}
 
template <typename ValueType, typename... Args>
AnyMovable::AnyMovable(std::in_place_type_t<ValueType> /*tag*/, Args&&... args)
    : content_(Holder<ValueType>::Make(std::forward<Args>(args)...)) {}
 
template <typename ValueType, typename Item, typename... Args>
AnyMovable::AnyMovable(std::in_place_type_t<ValueType> /*tag*/, std::initializer_list<Item> list, Args&&... args)
    : content_(Holder<ValueType>::Make(list, std::forward<Args>(args)...)) {}
 
template <typename ValueType>
AnyMovable& AnyMovable::operator=(ValueType&& rhs) {
    *this = AnyMovable(std::forward<ValueType>(rhs));
    return *this;
}
 
template <typename ValueType, typename... Args>
ValueType& AnyMovable::Emplace(Args&&... args) {
    content_ = Holder<ValueType>::Make(std::forward<Args>(args)...);
    return static_cast<Holder<ValueType>&>(*content_).held;
}
 
template <typename ValueType, typename Item, typename... Args>
ValueType& AnyMovable::Emplace(std::initializer_list<Item> list, Args&&... args) {
    content_ = Holder<ValueType>::Make(list, std::forward<Args>(args)...);
    return static_cast<Holder<ValueType>&>(*content_).held;
}
 
template <typename ValueType>
ValueType* AnyCast(AnyMovable* operand) noexcept {
    return AnyMovable::Holder<ValueType>::GetIf(operand);
}
 
template <typename ValueType>
const ValueType* AnyCast(const AnyMovable* operand) noexcept {
    return AnyMovable::Holder<ValueType>::GetIf(operand);
}
 
template <typename ValueType>
// might be requested by user
// NOLINTNEXTLINE(readability-const-return-type)
ValueType AnyCast(AnyMovable& operand) {
    using NonRef = std::remove_cv_t<std::remove_reference_t<ValueType>>;
    auto* result = AnyCast<NonRef>(&operand);
    if (!result) throw BadAnyMovableCast();
    return static_cast<ValueType>(*result);
}
 
template <typename ValueType>
// might be requested by user
// NOLINTNEXTLINE(readability-const-return-type)
ValueType AnyCast(const AnyMovable& operand) {
    using NonRef = std::remove_cv_t<std::remove_reference_t<ValueType>>;
    auto* result = AnyCast<NonRef>(&operand);
    if (!result) throw BadAnyMovableCast();
    return static_cast<ValueType>(*result);
}
 
template <typename ValueType>
ValueType AnyCast(AnyMovable&& operand) {
    using NonRef = std::remove_cv_t<std::remove_reference_t<ValueType>>;
    auto* result = AnyCast<NonRef>(&operand);
    if (!result) throw BadAnyMovableCast();
    return static_cast<ValueType>(std::move(*result));
}
 
}  // namespace utils
 
USERVER_NAMESPACE_END