kumi::projection_map< V > Class Template Reference

A stateless, compile-time schema for product type transformation. More...

#include <kumi/utils/projections.hpp>

Detailed Description

template<typename... V>
class kumi::projection_map< V >

A stateless, compile-time schema for product type transformation.

kumi::projection_map reifies the act of indexing or member access into a first-class type-level entity. It defines a sequence of accessors (projections) that can be applied to any kumi::product_type to extract, reorder, or reshape its components.

Because it is a "Meta-Product Type" (a product of accessors), it allows for complex data manipulations (like zipping or partitioning) to be expressed as a single Non-Type Template Parameter (NTTP).

Note

This type is stateless and carries zero runtime data.

Template Parameters

V	A pack of elements modeling kumi::concepts::projection.

Examples:

#include <kumi/kumi.hpp>
#include <iostream>
 
using namespace kumi::literals;
 
int main()
{
  std::cout << kumi::projection_map{0_c, "a"_id} << "\n";
  std::cout << kumi::projection_map{0_c, 1_c, kumi::projection_map{2_c, 3_c}} << "\n\n"; 
 
  // Projections maps can be built from functions in simpler cases 
  std::cout << kumi::indexes(0_c, 1_c, 2_c) << "\n\n";
  std::cout << kumi::identifiers("a"_id, "b"_id) << "\n";
}

Accessors
template<std::size_t I>
constexpr decltype(auto)	get (projection_map const &pm) noexcept
	Extracts the Ith element from a kumi::projection_map.

Properties
static constexpr auto	size () noexcept
	Returns the number of elements in a kumi::indexes_t.
static constexpr auto	empty () noexcept
	Returns true if a kumi::indexes_t contains 0 elements.