GenericMap.h

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// -*- LSST-C++ -*-
/*
 * This file is part of afw.
 *
 * Developed for the LSST Data Management System.
 * This product includes software developed by the LSST Project
 * (https://www.lsst.org).
 * See the COPYRIGHT file at the top-level directory of this distribution
 * for details of code ownership.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
#ifndef LSST_AFW_TYPEHANDLING_GENERICMAP_H
#define LSST_AFW_TYPEHANDLING_GENERICMAP_H
 
#include <algorithm>
#include <functional>
#include <memory>
#include <sstream>
#include <string>
#include <type_traits>
#include <utility>
#include <vector>
#include <variant>
 
#include "lsst/pex/exceptions.h"
#include "lsst/afw/typehandling/detail/type_traits.h"
#include "lsst/afw/typehandling/detail/refwrap_utils.h"
#include "lsst/afw/typehandling/Key.h"
#include "lsst/afw/typehandling/Storable.h"
#include "lsst/afw/typehandling/PolymorphicValue.h"
 
namespace lsst {
namespace afw {
namespace typehandling {
 
// TODO: correctly handling const vs. non-const keys should be possible in C++17 with std::variant
template <typename K>
class GenericMap {
public:
    using key_type = K;
    using size_type = std::size_t;
    using difference_type = std::ptrdiff_t;
 
    virtual ~GenericMap() noexcept = default;
 
    template <typename T, typename std::enable_if_t<!detail::IS_SMART_PTR<T>, int> = 0>
    T& at(Key<K, T> const& key) {
        // Both casts are safe; see Effective C++, Item 3
        return const_cast<T&>(static_cast<const GenericMap&>(*this).at(key));
    }
 
    template <typename T, typename std::enable_if_t<!detail::IS_SMART_PTR<T>, int> = 0>
    T const& at(Key<K, T> const& key) const {
        // Delegate to private methods to hide further special-casing of T
        return _at(key);
    }
 
    template <typename T, typename std::enable_if_t<std::is_base_of<Storable, T>::value, int> = 0>
    std::shared_ptr<T> at(Key<K, std::shared_ptr<T>> const& key) const {
        // Delegate to private methods to hide further special-casing of T
        return _at(key);
    }
 
    virtual size_type size() const noexcept = 0;
 
    virtual bool empty() const noexcept = 0;
 
    virtual size_type max_size() const noexcept = 0;
 
    template <typename T>
    size_type count(Key<K, T> const& key) const {
        return contains(key) ? 1 : 0;
    }
 
    virtual bool contains(K const& key) const = 0;
 
    template <typename T>
    bool contains(Key<K, T> const& key) const {
        // Delegate to private methods to hide special-casing of T
        return _contains(key);
    }
 
    virtual std::vector<K> const& keys() const noexcept = 0;
 
    virtual bool operator==(GenericMap const& other) const noexcept {
        auto keys1 = this->keys();
        auto keys2 = other.keys();
        if (!std::is_permutation(keys1.begin(), keys1.end(), keys2.begin(), keys2.end())) {
            return false;
        }
        for (K const& key : keys1) {
            // Can't use std::variant::operator== here because
            // std::reference_wrapper isn't equality-comparable.
            if (!detail::refwrap_equals()(this->unsafeLookup(key), other.unsafeLookup(key))) {
                return false;
            }
        }
        return true;
    }
 
    bool operator!=(GenericMap const& other) const { return !(*this == other); }
 
    template <class Visitor>
    auto apply(Visitor&& visitor) const {
        // Delegate to private methods to hide special-casing of Visitor
        return _apply(visitor);
    }
 
    template <class Visitor>
    auto apply(Visitor&& visitor) {
        // Delegate to private methods to hide special-casing of Visitor
        return _apply(visitor);
    }
 
private:
    // Transformations between value/reference/ref-to-const versions of internal variant type, to let
    //     the set of value types supported by GenericMap be defined only once
    // Icky TMP, but I can't find another way to get at the template arguments for variant :(
    // Methods have no definition but can't be deleted without breaking type definitions below
 
    template <typename... Types>
    static std::variant<std::reference_wrapper<Types>...> _typeToRef(
            std::variant<Types...> const&) noexcept;
    template <typename... Types>
    static std::variant<std::reference_wrapper<std::add_const_t<Types>>...> _typeToConstRef(
            std::variant<Types...> const&) noexcept;
 
protected:
    // Use int, long, long long instead of int32_t, int64_t because C++ doesn't
    // consider signed integers of the same length but different names equivalent
    using StorableType = std::variant<bool, int, long, long long, float, double, std::string,
                                      PolymorphicValue, std::shared_ptr<Storable const>>;
 
    // this mouthful is shorter than the equivalent expression with result_of
    using ConstValueReference = decltype(_typeToConstRef(std::declval<StorableType>()));
    using ValueReference = decltype(_typeToRef(std::declval<StorableType>()));
 
    virtual ConstValueReference unsafeLookup(K key) const = 0;
 
    ValueReference unsafeLookup(K key) {
        ConstValueReference constRef = static_cast<const GenericMap&>(*this).unsafeLookup(key);
        return std::visit(
            [](auto const & v) { return ValueReference(detail::refwrap_const_cast(v)); },
            constRef
        );
    }
 
private:
    // Neither Storable nor shared_ptr<Storable>
    template <typename T,
              typename std::enable_if_t<
                      std::is_fundamental<T>::value || std::is_base_of<std::string, T>::value, int> = 0>
    T const& _at(Key<K, T> const& key) const {
        static_assert(!std::is_const<T>::value,
                      "Due to implementation constraints, const keys are not supported.");
        auto foo = unsafeLookup(key.getId());
        if (std::holds_alternative<std::reference_wrapper<T const>>(foo)) {
            return std::get<std::reference_wrapper<T const>>(foo);
        } else {
            std::stringstream message;
            message << "Key " << key << " not found, but a key labeled " << key.getId() << " is present.";
            throw LSST_EXCEPT(pex::exceptions::OutOfRangeError, message.str());
        }
    }
 
    // Storable and its subclasses
    template <typename T, typename std::enable_if_t<std::is_base_of<Storable, T>::value, int> = 0>
    T const& _at(Key<K, T> const& key) const {
        static_assert(!std::is_const<T>::value,
                      "Due to implementation constraints, const keys are not supported.");
        auto foo = unsafeLookup(key.getId());
        if (std::holds_alternative<std::reference_wrapper<PolymorphicValue const>>(foo)) {
            Storable const& value = std::get<std::reference_wrapper<PolymorphicValue const>>(foo).get();
            T const* typedPointer = dynamic_cast<T const*>(&value);
            if (typedPointer != nullptr) {
                return *typedPointer;
            } else {
                std::stringstream message;
                message << "Key " << key << " not found, but a key labeled " << key.getId() << " is present.";
                throw LSST_EXCEPT(pex::exceptions::OutOfRangeError, message.str());
            }
        } else {
            std::stringstream message;
            message << "Key " << key << " not found, but a key labeled " << key.getId() << " is present.";
            throw LSST_EXCEPT(pex::exceptions::OutOfRangeError, message.str());
        }
    }
 
    // shared_ptr<Storable>
    template <typename T, typename std::enable_if_t<std::is_base_of<Storable, T>::value, int> = 0>
    std::shared_ptr<T> _at(Key<K, std::shared_ptr<T>> const& key) const {
        static_assert(std::is_const<T>::value,
                      "Due to implementation constraints, pointers to non-const are not supported.");
        auto foo = unsafeLookup(key.getId());
        if (std::holds_alternative<std::reference_wrapper<std::shared_ptr<Storable const> const>>(foo)) {
            auto pointer = std::get<std::reference_wrapper<std::shared_ptr<Storable const> const>>(foo).get();
            if (pointer == nullptr) {  // dynamic_cast not helpful
                return nullptr;
            }
 
            std::shared_ptr<T> typedPointer = std::dynamic_pointer_cast<T>(pointer);
            // shared_ptr can be empty without being null. dynamic_pointer_cast
            // only promises result of failed cast is empty, so test for that
            if (typedPointer.use_count() > 0) {
                return typedPointer;
            } else {
                std::stringstream message;
                message << "Key " << key << " not found, but a key labeled " << key.getId() << " is present.";
                throw LSST_EXCEPT(pex::exceptions::OutOfRangeError, message.str());
            }
        } else {
            std::stringstream message;
            message << "Key " << key << " not found, but a key labeled " << key.getId() << " is present.";
            throw LSST_EXCEPT(pex::exceptions::OutOfRangeError, message.str());
        }
    }
 
    // Neither Storable nor shared_ptr<Storable>
    template <typename T,
              typename std::enable_if_t<
                      std::is_fundamental<T>::value || std::is_base_of<std::string, T>::value, int> = 0>
    bool _contains(Key<K, T> const& key) const {
        // Avoid actually getting and casting an object, if at all possible
        if (!contains(key.getId())) {
            return false;
        }
 
        auto foo = unsafeLookup(key.getId());
        return std::holds_alternative<std::reference_wrapper<T const>>(foo);
    }
 
    // Storable and its subclasses
    template <typename T, typename std::enable_if_t<std::is_base_of<Storable, T>::value, int> = 0>
    bool _contains(Key<K, T> const& key) const {
        // Avoid actually getting and casting an object, if at all possible
        if (!contains(key.getId())) {
            return false;
        }
 
        auto foo = unsafeLookup(key.getId());
        auto refwrap = std::get_if<std::reference_wrapper<PolymorphicValue const>>(&foo);
        if (refwrap) {
            Storable const & value = refwrap->get();
            auto asT = dynamic_cast<T const*>(&value);
            return asT != nullptr;
        } else {
            return false;
        }
    }
 
    // shared_ptr<Storable>
    template <typename T, typename std::enable_if_t<std::is_base_of<Storable, T>::value, int> = 0>
    bool _contains(Key<K, std::shared_ptr<T>> const& key) const {
        static_assert(std::is_const<T>::value,
                      "Due to implementation constraints, pointers to non-const are not supported.");
        // Avoid actually getting and casting an object, if at all possible
        if (!contains(key.getId())) {
            return false;
        }
 
        auto foo = unsafeLookup(key.getId());
        if (std::holds_alternative<std::reference_wrapper<std::shared_ptr<Storable const> const>>(foo)) {
            auto pointer = std::get<std::reference_wrapper<std::shared_ptr<Storable const> const>>(foo).get();
            if (pointer == nullptr) {  // Can't confirm type with dynamic_cast
                return true;
            }
            std::shared_ptr<T> typedPointer = std::dynamic_pointer_cast<T>(pointer);
            // shared_ptr can be empty without being null. dynamic_pointer_cast
            // only promises result of failed cast is empty, so test for that
            return typedPointer.use_count() > 0;
        } else {
            return false;
        }
    }
 
    // Type alias to properly handle Visitor output
    // Assume that each operator() has the same return type; variant will enforce it
    template <class Visitor>
    using _VisitorResult = std::invoke_result_t<Visitor, K&&, bool&>;
 
    // No return value, const GenericMap
    template <class Visitor, typename std::enable_if_t<std::is_void<_VisitorResult<Visitor>>::value, int> = 0>
    void _apply(Visitor&& visitor) const {
        auto wrapped = detail::make_refwrap_visitor(std::forward<Visitor>(visitor));
        for (K const& key : keys()) {
            std::variant<K> varKey = key;
            std::visit(wrapped, varKey, unsafeLookup(key));
        }
    }
 
    // Return value, const GenericMap
    template <class Visitor,
              typename std::enable_if_t<!std::is_void<_VisitorResult<Visitor>>::value, int> = 0>
    auto _apply(Visitor&& visitor) const {
        std::vector<_VisitorResult<Visitor>> results;
        results.reserve(size());
        auto wrapped = detail::make_refwrap_visitor(std::forward<Visitor>(visitor));
        for (K const& key : keys()) {
            std::variant<K> varKey = key;
            results.emplace_back(std::visit(wrapped, varKey, unsafeLookup(key)));
        }
        return results;
    }
 
    // No return value, non-const GenericMap
    template <class Visitor, typename std::enable_if_t<std::is_void<_VisitorResult<Visitor>>::value, int> = 0>
    void _apply(Visitor&& visitor) {
        auto wrapped = detail::make_refwrap_visitor(std::forward<Visitor>(visitor));
        for (K const& key : keys()) {
            std::variant<K> varKey = key;
            std::visit(wrapped, varKey, unsafeLookup(key));
        }
    }
 
    // Return value, non-const GenericMap
    template <class Visitor,
              typename std::enable_if_t<!std::is_void<_VisitorResult<Visitor>>::value, int> = 0>
    auto _apply(Visitor&& visitor) {
        std::vector<_VisitorResult<Visitor>> results;
        results.reserve(size());
        auto wrapped = detail::make_refwrap_visitor(std::forward<Visitor>(visitor));
 
        for (K const& key : keys()) {
            std::variant<K> varKey = key;
            results.emplace_back(std::visit(wrapped, varKey, unsafeLookup(key)));
        }
        return results;
    }
};
 
template <typename K>
class MutableGenericMap : public GenericMap<K> {
protected:
    using typename GenericMap<K>::StorableType;
 
public:
    virtual ~MutableGenericMap() noexcept = default;
 
    virtual void clear() noexcept = 0;
 
    template <typename T>
    bool insert(Key<K, T> const& key, T const& value) {
        if (this->contains(key.getId())) {
            return false;
        }
 
        return unsafeInsert(key.getId(), StorableType(value));
    }
 
    template <typename T>
    std::pair<Key<K, T>, bool> insert(K const& key, T const& value) {
        auto strongKey = makeKey<T>(key);
        // Construct return value in advance, so that exception from copying/moving Key is atomic
        auto result = make_pair(strongKey, false);
        result.second = insert(strongKey, value);
        return result;
    }
 
    template <typename T>
    bool erase(Key<K, T> const& key) {
        if (this->contains(key)) {
            return unsafeErase(key.getId());
        } else {
            return false;
        }
    }
 
protected:
    virtual bool unsafeInsert(K key, StorableType&& value) = 0;
 
    virtual bool unsafeErase(K key) = 0;
};
 
}  // namespace typehandling
}  // namespace afw
}  // namespace lsst
 
#endif