How Can a Proxy Class Enforce Binary Digit Restriction in an Array?

The Role of Proxy Class in C

In software engineering, a proxy class is a concept used to mediate access to an existing object, referred to as the "subject." The proxy class provides an altered interface, granting controlled and often limited interaction with the subject.

Purpose of Proxy Classes

Proxy classes are created for various reasons, including:

• Enhanced Access Control: Proxy classes can restrict access to certain methods or properties of the subject, allowing only specific operations to be performed. This is useful for enforcing security measures or hiding complex implementation details from the client.
• Lazy Loading: Proxy classes can be used to delay the creation or loading of the subject object until it is actually required. This optimization can improve performance, particularly if the subject involves resource-intensive operations.
• Synchronization: Proxy classes can be employed to manage concurrent access to the subject object, ensuring that multiple clients do not access the subject simultaneously.
• Logging and Debugging: Proxy classes can intercept method calls and log or print debugging information, helping to diagnose issues or monitor the system's behavior.

Example: Binary Digit Restriction

Consider the following example:

struct array1 {
    int mArray[10];
    int &operator[](int i) {
      /// what to put here
    }
};

In this example, we want to modify the Array class such that it can only contain binary digits (1 or 0). Implementing this directly in the Array's operator[] method would not be feasible because it cannot access the value being stored.

To solve this, we can introduce a proxy class:

struct aproxy {
    aproxy(int& r) : mPtr(&r) {}
    void operator = (int n) {
        if (n > 1 || n < 0) {
            throw "not binary digit";
        }
        *mPtr = n;
    }
    int * mPtr;
};

struct array {
    int mArray[10];
    aproxy operator[](int i) {
        return aproxy(mArray[i]);
    }
};

In this case, the Proxy class (aproxy) checks for invalid values (non-binary digits) and throws an exception if encountered. By making the Array's operator[] return an instance of the Proxy class, we enforce the binary digit restriction while still allowing access to the array elements.

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