MetaArray

This project is a small C++17 helper class that allows to create and modify a variadic template parameter easily.

I always understand everythong better if it's an example, so here it goes (this code does NOT compile, they are separate code parts)

Installation

Download the file MetaArray.cxx to your project and import it as a header.

Define the array

// Our array (is usefull to make an alias if you are going to use it a lot [like here])
// All other examples use this class
using MyArray = MetaArray<int, 0, 1, 2, 3, 4, 5, 6>;

Values

All this values are defines as static constexpr, so they can be used as template arguments.

// How many values we have
MyArray::size      // 7
// values is the array of the values (for an empty array, values is nullptr)
MyArray::values[2] // 2

Transformations

typename MyArray::template PushFront<24> // MetaArray<int, 24, 0, 1, 2, 3, 4, 5, 6>
typename MyArray::template PushBack<24>  // MetaArray<int, 0, 1, 2, 3, 4, 5, 6, 24>
typename MyArray::RemoveFront            // MetaArray<int, 1, 2, 3, 4, 5, 6>
typename MyArray::RemoveBack             // MetaArray<int, 0, 1, 2, 3, 4, 5>
typename MyArray::Reverse                // MetaArray<int, 6, 5, 4, 3, 2, 1, 0>

Forward the result to another class

template <typename T, T ... array> // It requires this template parameters
struct Example {
  // [...]
};

typename MyArray::RemoveFront::Reverse::Forward<Example> // Example<int, 6, 5, 4, 3, 2, 1>

Some times you want to have a different template parameters in the class. Sometimes, it can easily be solved by using an alias:

template<bool enabled, int ... values>
struct Example2 {
  // [...]
};

template <typename T, T ... array>
using Example2_From_Array = Example2<true, array...>; // Error if T is not int

typename MyArray::Reverse::template Forward<Example2_From_Array> // Example2<true, 6, 5, 4, 3, 2, 1, 0>

For more even more complex cases, you can use a helper struct:

#include <type_traits> // std::is_same_v

template <typename T, T ... array>
struct Example2_Builder {
  // Make the error readable
  static_assert(std::is_same_v<T, int>, "Wrong array type.");
  
  template <bool enabled>
  using Result = Example2<enabled, array...>;
};

typename MyArray::template Forward<Example2_Builder>::template Result<true> // Example2<true, 0, 1, 2, 3, 4, 5, 6>
typename MyArray::template Forward<Example2_Builder>::template Result<false> // Example2<false, 0, 1, 2, 3, 4, 5, 6>