inclusive_scan_left() [1/2]

template<typename Function, concepts::product_type T, typename Value>

auto kumi::inclusive_scan_left ( Function f, T && t, Value init )

inlinenodiscardconstexpr

Computes the inclusive prefix scan of all elements of a product type using a tail recursive call.

On record types, this function operates on the underlying values, not on the fields themselves.

Note

The first stored value is the result of the application of the function to the provided initial value and the first element of the product_type.

Parameters

f	Binary callable function to apply
t	Product type to operate on
init	Optional initial value of the scan

Returns

A tuple of prefix partial accumulations where each element 'I' equals f( f( f(init, get<0>(t)), ...), get<I-1>(t))

Helper type

namespace kumi::result
{
  template<typename Function, product_type T, typename Value> struct inclusive_scan_left;
 
  template<typename Function, product_type T, typename Value>
  using inclusive_scan_left_t = typename inclusive_scan_left<Function,T,Value>::type;
}

Computes the return type of a call to kumi::inclusive_scan_left

Examples:

Tuple:

#include <kumi/kumi.hpp>
#include <iostream>
 
int main()
{
  auto t = kumi::tuple{2.,1,short{55},'z'};
 
  auto output = kumi::inclusive_scan_left( [](auto acc, auto elt) 
                  { 
                    return acc + sizeof(elt); 
                  }
                  , t
                  , std::size_t{42}                
                );
 
  std::cout << output << "\n"; 
 
  auto u = kumi::tuple{1,3,2,4,0,5,9,6,7};
 
  std::cout << kumi::inclusive_scan_left(kumi::function::plus, u) << "\n";
}

Record:

#include <kumi/kumi.hpp>
#include <iostream>
 
int main()
{
  using namespace kumi::literals;
  auto r = kumi::record{"a"_id = 2.,"b"_id = 1,"c"_id = short{55},"d"_id = 'z'};
 
  auto output = kumi::inclusive_scan_left( [](auto acc, auto elt) 
                  { 
                    return acc + sizeof(elt); 
                  }
                  , r
                  , std::size_t{42}                
                );
 
  std::cout << output << "\n"; 
 
  auto u = kumi::record{"a"_id = 1,"b"_id = 3,"c"_id = 2,"d"_id = 4,"e"_id = 0
                      ,"f"_id = 5,"g"_id = 9,"h"_id = 6,"i"_id = 7};
 
  std::cout << kumi::inclusive_scan_left(kumi::function::plus, u) << "\n";
}