无法专门化std :: hash来存储unordered_map中的自定义类型

Question

我正在尝试使用共享库中定义的类的实例作为unordered_map的键。但是当我以常规，正确的方式专门为这个名为Tile的类专门设计std :: hash模板时，由于某种原因，编译器一直在抱怨：

/usr/include/c++/7/bits/hashtable_policy.h:87: error: no match for call to ‘(const std::hash<Tile>) (const Tile&)’
  noexcept(declval<const _Hash&>()(declval<const _Key&>()))>
           ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~

这是头文件，我在其中定义了std :: hash（pathfinder.h）的特化：

#ifndef PATHFINDER_H
#define PATHFINDER_H

#include <vector>
#include <unordered_set>
#include <unordered_map>
#include <memory>

#include "Libworld/world.h"
#include "node.h"
#include "nodifier.h"
#include "pathgenerator.h"

namespace std {
    template <>
    struct hash < Tile > {
        public:
            size_t operator() ( const Tile & theTile ) const noexcept {
               return ( ( 32768 * theTile.getXPos ( ) ) + theTile.getYPos ( ) );
            }
            size_t operator() ( const Tile * theTile ) const noexcept {
               return ( ( 32768 * theTile->getXPos ( ) ) + theTile->getYPos ( ) );
            }
    };

    template <>
    struct equal_to < Tile > {
        bool operator ( ) ( const Tile & lhs, const Tile & rhs ) const {
            return ( lhs == rhs );
        }
    };
}

class Pathfinder {
    private:
        std::vector < std::unique_ptr < Tile > > theWorld;
        QString theWorldName;
        int worldRows, worldColumns, numberOfEnemies, numberOfHealthPacks;

        std::unordered_set < std::shared_ptr < Node > > worldNodes;
        std::unordered_map < Tile, bool > hasEnemyOrHealthPack;

        std::shared_ptr < Nodifier > worldNodifier;
        std::shared_ptr < PathGenerator > worldPathGenerator;

        Tile startingTile, endingTile;
        std::shared_ptr < Node > startingNode, endingNode;

        // unsigned int findTileWithLocation ( std::vector < std::unique_ptr < Node > > * nodesList, int x, int y ) const;

        void generateNodes ( );
        void generateHasEnemyOrHealthPack ( World worldLoader, int numberOfEnemies, int numberOfHealthPacks );

public:
    Pathfinder ( QString initialWorldName,
                 Tile initialStartingTile,
                 Tile initialEndingTile,
                 std::shared_ptr < Nodifier > initialWorldNodifier,
                 std::shared_ptr < PathGenerator > initialWorldPathGenerator,
                 int initialNumberOfEnemies,
                 int initialNumberOfHealthPacks );

    QString getWorldName ( ) const;
    void loadNewWorld ( const QString & newWorldName );
    void loadNewWorld ( const QString & newWorldName, const Tile & newWorldStartingTile, const Tile & newWorldEndingTile );

    Tile getStartingTile ( ) const;
    void setStartingTile ( const Tile & newStartingTile );
    Tile getEndingTile ( ) const;
    void setEndingTile ( const Tile & newEndingTile );
    std::shared_ptr < Nodifier > getWorldNodifier ( ) const;
    void setWorldNodifier ( const std::shared_ptr < Nodifier > & newWorldNodifier );
    Tile getTileFromWorld ( int x, int y );

    void printNodes ( );
    void printWorld ( );

    std::list < std::pair <int, int> > generatePath ( );
};

#endif

这是包含Tile定义的共享库的头文件：

#ifndef WORLD_H
#define WORLD_H

#include "world_global.h"
#include <vector>
#include <memory>
#include <QObject>
#include <QImage>

class Tile
{
public:
    Tile(int xPosition, int yPosition, float tileWeight);
    virtual ~Tile() =default;
    float getValue() const {return value;};
    void setValue(float newValue) {value = newValue;};
    int getXPos() const {return xPos;};
    int getYPos() const {return yPos;};
    void setXPos(int newPos) {xPos = newPos;};
    void setYPos(int newPos) {yPos = newPos;}
    bool operator== (const Tile & other) const
        {return (getXPos() == other.getXPos()) && (getYPos() == other.getYPos());};

protected:
    int xPos;
    int yPos;
    float value;
};

class Enemy : public Tile
{
public:
    Enemy(int xPosition, int yPosition, float strength);
    virtual ~Enemy() = default;
    bool getDefeated() const {return defeated;}
    void setDefeated(bool value) {defeated = value;};

private:
    bool defeated; //false by construction
};

class PEnemy: public QObject, public Enemy
{
    Q_OBJECT
public:
    PEnemy(int xPosition, int yPosition, float strength);
    virtual ~PEnemy() = default;
    float getPoisonLevel() const;
    void setPoisonLevel(float value);

public slots:
    bool poison();

signals:
    void dead();
    void poisonLevelUpdated(int value);

private:
    float poisonLevel;
};

class Protagonist: public QObject, public Tile
{
    Q_OBJECT
public:
    Protagonist();
    void setXPos(int newPos) {xPos = newPos; emit posChanged(xPos, yPos);}
    void setYPos(int newPos) {yPos = newPos; emit posChanged(xPos, yPos);}
    void setPos(int newX, int newY) {if (xPos != newX || yPos != newY) {xPos = newX; yPos = newY; emit posChanged(xPos, yPos);}}
    float getHealth() const {return health;};
    void setHealth(float value) {health = value;}

    float getEnergy() const {return energy;}
    void setEnergy(float value) {energy = value;}

signals:
    void posChanged(int x, int y);

private:
    float health; //100.0f by construction
    float energy; //100.0f by construction
};

class WORLDSHARED_EXPORT World
{
public:
    World() = default;
    //to obtain non-overlapping enemies and healthpacks you should call the following 3 methods in this order
    std::vector<std::unique_ptr<Tile>> createWorld(QString filename);
    std::vector<std::unique_ptr<Enemy>> getEnemies(unsigned int nrOfEnemies);
    std::vector<std::unique_ptr<Tile>> getHealthPacks(unsigned int nrOfPacks);
    std::unique_ptr<Protagonist> getProtagonist();
    int getRows() const {return rows;};
    int getCols() const {return cols;};

private:
    int rows, cols;
    QImage world;
    std::vector<QPoint> used; //only for internal use
};


#endif // WORLD_H

我确定我正在做的一切正确，所以我很乐意，如果有人能告诉我为什么这不能编译？

非常感谢提前，我一直坚持这一点。

最好的问候，约书亚

Answer 1

如果我将templahttps：//stackoverflow.com/help/how-to-answerte specialized移动到定义了Tile类的头文件中（当然是在定义类之后，但之后的ANYWHERE），代码将编译。

通常，当您自己实施课程时，这也无关紧要。我认为这与在共享库中实现的这个类有关。我不是C ++大师，所以我无法解释这一点。但是我想在这里有人还在解释它。