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Language: C++
Expertise: Intermediate

Oct 30, 2000

Suppose you are writing a method in a class that accepts a parameter of a given type. Such a method can also be called with an argument of a different type—as long as an implicit conversion exists between the two types (for example, short to int).

 class example
{
public:
    void method(int parameter);
    ...
}

int main()
{
	example eg;
	short pants = 42;
	eg.method(pants); // short to int conversion here
	...
	return 0;
}

It is possible to overload such methods, and by making the overloaded method private, unwanted conversions can be turned into compile time errors. For example:

 
class example
{
public:
    void method(int parameter);
    ..
private: // reject unwanted conversions 
    void method(short);
    ...
}

int main()
{
	example eg;
	short pants = 42;
	eg.method(pants); // Compile time error
	...
	return 0;
}

You can even use this technique to overload on different signedness of integers. For example:

 
namespace non_std
{
    class string
    {
    public:
              char & operator[](size_t index);
        const char & operator[](size_t index) const;
    ..
    private: // reject unwanted conversions 
        void operator[](signed int);
        void operator[](signed int) const;
    ...
    };
}