How Can Key-Oriented Access Protection Be Improved in C 03 and C 0x?

Enhancements for Re-usable Key-Oriented Access Protection

Introduction

In response to a previous question regarding re-usability of a key-oriented access-protection pattern, this discussion investigates improvements and potential enhancements.

Proposed Improvement for Standard C 03

To enhance the pattern in standard C 03, a macro-based solution is introduced. This approach introduces EXPAND for template parameter expansion and PASSKEY macros for defining passkeys with friend classes. While this simplifies passkey definitions, it still requires callers to specify the passkey they need. Additionally, the macro syntax may be considered cumbersome.

Significant Advancements in C 0x

C 0x introduces significant advancements that simplify the pattern. Variadic templates enable functions to declare their own passkeys and allow template parameters to be friends. These features allow for a highly expressive and generic solution.

The updated pattern utilizes the passkey template and a allow class. passkey associates itself with a specific class or function, allowing that class or function exclusive access. allow verifies that a passkey is authorized, based on the keys specified in its template parameters.

Advantages of C 0x Solution

The C 0x solution offers several benefits:

• Simplified Key Creation: Callers no longer need to specify specific passkeys. Classes have their own unique passkeys, and functions declare the passkeys they accept.
• Generic Implementation: The pattern is implemented generically, requiring no additional definitions in most scenarios.
• Enforced Key Restrictions: The allow class ensures that only authorized passkeys can be used.
• Single Boilerplate Code: Only boilerplate code needs to be defined once, and it handles all key-oriented access protection.

Conclusion

The proposed improvements for Standard C 03 and C 0x significantly enhance the re-usability and expressiveness of the key-oriented access-protection pattern. The C 0x solution, in particular, offers a highly generic and convenient implementation.

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