How Can C 11\'s \'Passkey\' Pattern Enhance Access Control?

Access Protection through Key-Oriented Idiom

In a prior discussion, Matthieu M. introduced a technique for access protection based on key-oriented idiomatic usage. While previously encountered, the pattern had not been explicitly recognized as such.

The concept involves defining a class (SomeKey) as a key, which grants access to a protected method (protectedMethod) in a separate class (Bar) only to those classes that are friends with the key class (Foo in this example). Specifically, while Foo can invoke protectedMethod using a key instance, classes lacking such friendship, such as Baz, are restricted from accessing it.

This approach enables fine-grained access control, surpassing the need for designating Foo as a friend of Bar or using more intricate proxy patterns.

Pattern Identification

The referenced technique is now widely known as the "passkey" pattern. This name emerged as the most prevalent during subsequent inquiries.

C 11 Simplification

In C 11, the pattern becomes even more elegant. Instead of calling b.protectedMethod(SomeKey());, you can simply write b.protectedMethod({});, further enhancing its ease of implementation.

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