c++是否可以将对象类型传递给要与之比较的函数

Question

我遇到这样一种情况，我需要查明派生对象是否存储在另一个对象的 vector 中，并想对其进行功能化。我想不出一种方法来做我想做的事情，或者确定它是否可行。我有一个有效的解决方案，我将其包括在内，但如果有一种直接的方法来实现目标，它会更清晰。

这基本上就是我想做的:

class IFruit
{
public:
    virtual ~IFruit(){};
};
class Apple : public IFruit {};
class Banana : public IFruit {};
class Orange : public IFruit {};

class FruitBowl
{
public:
    bool HasFruit( datatype?? FruitType )
    {
        for ( auto iter : m_Fruit )
        {
            if ( typeof( iter ) == typeof( FruitType ) )
            {
                return ( true );
            }
        }
        return ( false );
    }

    vector< IFruit* > m_Fruit;
};

int main()
{
    FruitBowl Snacks;
    Snacks.m_Fruit.push_back( new Banana );
    Snacks.m_Fruit.push_back( new Apple );
    Snacks.m_Fruit.push_back( new Orange );

    if ( Snacks.HasFruit( Orange ) )
    {
        cout << "There is an orange available";
    }

    return ( 0 );
}

这是实现目标的解决方法，但它有提供回调的额外步骤，我很想根除它:

#include <vector>
#include <iostream>
#include <functional>
using namespace std;

class IFruit
{
public:
    virtual ~IFruit(){};
};
class Apple : public IFruit {};
class Banana : public IFruit {};
class Orange : public IFruit {};

class FruitBowl
{
public:
    bool HasFruit( function< bool( IFruit* ) > fnCompareFruitType )
    {
        for ( auto iter : m_Fruit )
        {
            if ( fnCompareFruitType( iter ) )
            {
                return ( true );
            }
        }
        return ( false );
    }

    vector< IFruit* > m_Fruit;
};

int main()
{
    FruitBowl Snacks;
    Snacks.m_Fruit.push_back( new Banana );
    Snacks.m_Fruit.push_back( new Apple );
    Snacks.m_Fruit.push_back( new Orange );

    if ( Snacks.HasFruit( []( IFruit* TestFruit ){ return ( dynamic_cast< Orange* >( TestFruit ) != nullptr ); } ) )
    {
        cout << "There is an orange available";
    }

    return ( 0 );
}

Answer 1

您不能将类型作为运行时函数参数传递，但可以将类型用作函数模板的编译时模板参数:

#include <vector>
#include <iostream>
#include <algorithm>

class IFruit
{
public:
    virtual ~IFruit(){};
};
class Apple : public IFruit {};
class Banana : public IFruit {};
class Orange : public IFruit {};

class FruitBowl
{
public:
    template <typename T>
    bool HasFruit()
    {
        return std::any_of(m_Fruit.begin(), m_Fruit.end(),
                          [](IFruit* fruit) {
                              return dynamic_cast<T*>(fruit) != nullptr;
                          });
    }

    std::vector< IFruit* > m_Fruit;
};


int main()
{
    FruitBowl Snacks;
    Snacks.m_Fruit.push_back( new Banana );
    Snacks.m_Fruit.push_back( new Apple );
    Snacks.m_Fruit.push_back( new Orange );

    if ( Snacks.HasFruit<Orange>() )
    {
        std::cout << "There is an orange available";
    }
}