Polymorphic span

A tiny header-only C++ library extending std::span concept for polymorphic object types. Make your interfaces nicer!

Motivation

void doWork(std::span<const int> myData);

Thanks to std::span the function takes input stored in different containers, "storage" and "access" aspects of the input data are decoupled and the interface is clean. No performance overhead, the function is not a template.

C++ is an object-oriented programming language and you might have objects with inheritance hierarchy. Let Cat and Dog are derived from Animal and stored as std::vector<Cat> and std::array<Dog, 5>. How to define argument for a function taking Animals stored in a buffer? You're forced to use templates and write something super-generic like this:

template <typename InputIterator>
int countHungryAnimals(InputIterator animalBegin, InputIterator animalEnd);

C++20 makes it nicer with Ranges, but still it needs templates and so the code can't be moved to a .cpp file, what causes drawbacks such as slow compilation.

Can we make it better? Yes, let's use poly_span:

#include "span/poly_span.h"

int countHungryAnimals(span::poly_span<const Animal> animals);

Similar to std::span and iterators it's flexible to how the objects are stored, the interface is clean and the function is not a template. poly_span will take std::vector, std::array, gsl::span, C array, iterators and pointers of types derived from Animal. Cool, isn't?

poly_span is lightweight wrapper, no dynamic allocation, no virtual functions, just pointer arithmetic.

How to build and use

It's a header-only library, no third-party dependencies, works with C++11 and above. Just add include dir to your project's include search path.

To build and run the tests please do:

git clone ... your_dir
cd your_dir && mkdir build && cd build
cmake .. && cmake --build .
ctest

License

This project is licensed under the MIT License

Author

Dr. Alexander Bulovyatov.

Please share your opinion and ideas to bulovyatov AT g m a i l . c o m