What is a Proxy Class in C and How Does It Work?

Proxy Class in C : Understanding Purpose and Implementations

In object-oriented programming, a proxy class is a fundamental design pattern that provides an alternative interface to another class, the target class. The proxy acts as an intermediary, allowing interactions with the target class in a controlled and customized manner.

Purpose of Proxy Class

Proxy classes are primarily used to:

• Provide Controlled Access: They restrict access to the target class's sensitive or expensive operations.
• Add Functionality: They enhance the target class with additional functionalities, such as caching or security checks.
• Handle Complexity: They simplify the interactions with complex target classes by presenting a simpler interface.

Where Proxy Classes are Useful

Proxy classes prove valuable in various scenarios:

• Lazy Initialization: Delaying the creation of expensive objects until needed.
• Session Management: Controlling access to a resource during a particular session.
• Virtual Proxy: Providing a temporary representation of an object before it is actually created.
• Remote Proxy: Facilitating communication between objects residing in different processes or machines.

Example: Binary Array Proxy

To illustrate the concept of a proxy class, consider a scenario where we need an array that can only store binary digits (0 or 1). A naive implementation would look something like this:

struct array1 {
    int mArray[10];
    int &operator[](int i) { /* Implementation here */ }
};

However, this implementation lacks the ability to enforce the binary digit constraint. To address this, we create a proxy class:

struct aproxy {
    aproxy(int& r) : mPtr(&r) {}
    void operator = (int n) { /* Enforce binary digit constraint here */ }
    int *mPtr;
};

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

In this example, the aproxy class acts as the proxy, providing controlled access to the mArray element via its overloaded assignment operator. This allows us to enforce the binary digit constraint in the proxy class, ensuring that only valid values are stored in the array.

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