How Can C Achieve Type Erasure: A Guide to Common Techniques?

Type Erasure Techniques in C

Type erasure refers to the process of hiding type information about a class, enabling the manipulation of objects without exposing their underlying types. This article explores various type erasure techniques and their functionality.

Common Techniques:

1. Virtual Functions:
Virtual functions encapsulate behavior in an interface-based hierarchy. Implementing classes hide their implementation details, allowing the invocation of virtual functions polymorphically.

2. Function Pointers:
Function pointers can represent templated functions. Objects are held in void* pointers to hide their types. This technique is used in Boost.Function libraries.

3. shared_ptr:
shared_ptr offers a unique approach to type erasure. It enables storing objects of any type and automatically invokes the correct destructor. The shared_ptr constructor template generates the deleter based on the actual object's type.

4. "GMan" Technique:
This technique uses intermediate delegates and exploits a double template instantiation to effectively hide the actual type behind a movable delegate, allowing for type-safe operations and method invocation.

Use Cases:

• Object pooling
• Polymorphic factories
• Runtime polymorphism without inheritance
• Hiding implementation details for improved flexibility and maintainability

Example Code:

The provided example code demonstrates the Any_Virtual and Any_VoidPtr type erasure techniques in action. It allows the storage and manipulation of objects with different types while hiding their actual types behind virtual functions or void* pointers and function pointers.

Further Reading:

• [Boost.Any Reference](https://www.boost.org/doc/libs/1_55_0/libs/any/doc/html/index.html)
• [Function Pointers in C ](https://www.learncpp.com/cpp-tutorial/function-pointers-in-cpp/)
• [GMan's Delegate-Based Technique](https://codereview.stackexchange.com/questions/56752/generic-function-with-hidden-type-information-in-c)

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