How Can C Achieve Type Erasure: A Comparison of Techniques?

Type Erasure Techniques in C

Type erasure in C refers to the technique of hiding some or all of the type information regarding a class, similar to Boost.Any. Here are various type erasure approaches:

Virtual Functions

Virtual functions are a classic technique where you abstract the implementation of a class inside an interface-based class hierarchy. This approach is adopted by many Boost libraries, such as Boost.Any and Boost.Shared_ptr, to hide types or deallocation mechanisms.

Function Pointers with Templated Functions

An alternative option involves using function pointers with templated functions, while storing the actual object in a void* pointer. Boost.Function utilizes this technique to conceal the real type of a functor.

Template-based Type Erasure without Virtual Functions or Void* Manipulation

For instance, GMan's approach utilizes templates to hide actual types without resorting to virtual functions or void* manipulation.

Shared_Ptr

shared_ptr is a particularly intriguing technique. It leverages function templates in the shared_ptr constructor to store any data and appropriately call the correct destructor at the end. Despite its simplicity, this approach offers convenience by packaging the traditional void*/function-pointer type erasure concept.

Comparison of Techniques

All type erasure techniques in C employ function pointers and void* pointers, with the primary difference being in the provision of semantic sugar.

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