PolicyCB

PolicyCB is a C++20 library that provides a flexbible Callback implementation. This is a highly experimental implementation and shouldn't be use in any production environment. View the associated Blog post for more details. Users may configure the behavior of the class via the below template parameters:

// The policy on allowed callable and Callback itself
// Note that when none of them is DYNAMIC, Callback<> could
// utilize flattened function pointer to save a virtual call
// @{
enum class MovePolicy
{
    // Allows non-trivially movable object
    DYNAMIC = 0,
    // Only allows trivially movable object
    TRIVIAL_ONLY = 1,
    // Forbids any move on Callback
    NOMOVE = 2,
};

enum class CopyPolicy
{
    // Allows non-trivially copyable object
    DYNAMIC = 0,
    // Only allows trivially copyable object
    TRIVIAL_ONLY = 1,
    // Forbids any copy on Callback
    NOCOPY = 2,
};

enum class DestroyPolicy
{
    // Allows non-trivially destructable object
    DYNAMIC = 0,
    // Only allows trivially destructable object
    TRIVIAL_ONLY = 1,
};

// @}

// Policy on the small-buffer-optimization storage
enum class SBOPolicy
{
    // Allows the Callback to store arbitrary-sized object
    // The storage takes InitialBufferSize + 8 bytes
    DYNAMIC_GROWTH = 0,
    // Only allows the Callback to store a object with specified
    // maximum size. Causes an compilation error if the object is
    // too large.
    FIXED_SIZE = 1,
    // This disables storage of the original function,
    // essentially makes the Callback a function pointer
    NO_STORAGE = 2,
};


template<typename FT, // function signature
         MovePolicy MP,
         CopyPolicy CP,
         DestroyPolicy DP,
         SBOPolicy SBOP,
         std::size_t InitialBufferSize = 16>
class Callback;

This is a header-only library. Drop in include/PolicyCB.hpp into your project to use it.

License

Apache 2.0