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Generic Methods

 

Introduction

We saw that you could create a function as a generic. When it comes to a class, one of the most fundamental ways you can involve a generic is to implement the method of a class as a generic. You can do this by preceding the definition of the method with the declaration of a generic, exactly as we did in the previous sections. Here is an example:

public ref class General
{
public:
    generic <class T>
    void Show()
    {
    }
};

Passing a Parameter Type

If you plan to process a value of the parameter type in the method, you can pass an argument to the method. Here is an example:

public ref class General
{
public:
    generic <class T>
    void Show(T value)
    {
    }
};

In the body of the method, you can use the argument as you see fit. As we saw in the previous lesson and in the previous sections, at a minimum, you can display the value of the argument by passing it to the Console::WriteLine() method. Before calling the method, you can first declare a variable or a handle of the class. You can then call the method using the period or the arrow operator. Here are examples:

using namespace System;

public ref class General
{
public:
    generic <class T>
    void Show(T value)
    {
        Console::WriteLine(value);
    }
};

int main()
{
    // Call the version of the function that displays an integer
    int Integer = 246;
    General gen;
    Console::Write(L"Value: ");
    gen.Show<int>(Integer);

    // Call the version of the function that displays a character
    __wchar_t Character = L'G';
    Console::Write(L"Value: ");
    gen.Show<__wchar_t>(Character);

    // Call the version of the function that displays a decimal
    double DoublePrecision = 355.65;
    Console::Write(L"Value: ");
    gen.Show<double>(DoublePrecision);

    return 0;
}

This would produce:

Value: 246
Value: G
Value: 355.65
Press any key to continue . . .

If you want to implement the method outside of its class, make sure you precede it with the generic declaration. Here is an example:

using namespace System;

public ref class General
{
public:
    generic <class T>
    void Show(T value);
};

generic <class T>
void General::Show(T value)
{
    Console::WriteLine(value);
}

int main()
{
    return 0;
}

Remember that you can also declare a class on the managed heap using the gcnew operator and access its member(s) using the -> operator:

using namespace System;

public ref class General
{
public:
    generic <class T>
    void Show(T value);
};

generic <class T>
void General::Show(T value)
{
    Console::WriteLine(value);
}

int main()
{
    // Call the version of the function that displays an integer
    int Integer = 246;
    General ^ gen = gcnew General;
    Console::Write(L"Value: ");
    gen->Show<int>(Integer);

    // Call the version of the function that displays a character
    __wchar_t Character = L'G';
    Console::Write(L"Value: ");
    gen->Show<__wchar_t>(Character);

    // Call the version of the function that displays a decimal
    double DoublePrecision = 355.65;
    Console::Write(L"Value: ");
    gen->Show<double>(DoublePrecision);

    return 0;
}

A generic method can also be declared as static, in which case you would access it using the :: operator. Here is an example:

using namespace System;

public ref class General
{
public:
    generic <class T>
    static void Show(T value)
    {
        Console::WriteLine(value);
    }
};

int main()
{
    // Call the version of the function that displays an integer
    Console::Write(L"Value: ");
    General::Show<int>(246);

    // Call the version of the function that displays a character
    Console::Write(L"Value: ");
    General::Show<__wchar_t>(L'G');

    // Call the version of the function that displays a decimal
    Console::Write(L"Value: ");
    General::Show<double>(355.65);

    return 0;
}

Returning a Parameter Type

After setting a generic declaration before a method, just as you can pass it as argument, you may want the method to return a value of the parameter type. To do this, simply specify the return type. Here is an example:

public ref class General
{
public:
    generic <class T>
    void Show(T value);

    generic <class T>
    T GetValue();
};

When implementing the method, make sure you return the parameter type before the method exits. Here is an example:

generic <class T>
T General::GetValue()
{
    T val;

    return val;
}
 

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