Reduce and Mixed Data Types

std::reduce() is designed to work with a range of elements that are generally of the same type, but it can handle mixed data types with some considerations.

The key is that the binary operation used in std::reduce() must be able to accept and return the appropriate types.

If you have a collection of mixed data types, you need to ensure that the operation you provide can handle these types correctly.

One common approach is to use a std::variant or a custom struct to encapsulate the different types.

Here's an example using a custom struct to handle a mix of integers and floats:

1#include <iostream>
2#include <numeric>
3#include <variant>
4#include <vector>
5
6struct Mixed {
7  int intValue;
8  float floatValue;
9};
10
11Mixed addMixed(const Mixed& a, const Mixed& b) {
12  return {
13    a.intValue + b.intValue,
14    a.floatValue + b.floatValue
15  };
16}
17
18int main() {
19  std::vector<Mixed> numbers{
20    {1, 1.1f}, {2, 2.2f}, {3, 3.3f}};
21
22  Mixed result = std::reduce(
23    numbers.begin(),
24    numbers.end(),
25    Mixed{0, 0.0f},
26    addMixed
27  );
28
29  std::cout << "Int Result: "
30    << result.intValue << "\n";
31  std::cout << "Float Result: "
32    << result.floatValue << '\n';
33}

1Int Result: 6
2Float Result: 6.6

In this example, Mixed is a struct that holds both an integer and a float. The addMixed function defines how two Mixed objects should be combined.

When calling std::reduce(), we pass Mixed{0, 0.0f} as the initial value and addMixed as the binary operation.

For simpler cases, if the mixed types are compatible with basic arithmetic operations, you can use std::variant with a lambda to handle the combination:

1#include <iostream>
2#include <numeric>
3#include <variant>
4#include <vector>
5
6using Mixed = std::variant<int, float>;
7
8float addMixed(float a, const Mixed& b) {
9  return a + std::visit([](auto&& value) {
10    return static_cast<float>(value);
11  }, b);
12}
13
14int main() {
15  std::vector<Mixed> numbers{1, 2.2f, 3};
16
17  float result = std::reduce( numbers.begin(),
18    numbers.end(), 0.0f, addMixed);
19
20  std::cout << "Result: " << result;
21}

1Result: 6.2

This approach uses std::variant to handle different types and std::visit() to apply the correct operation within the lambda.

In summary, std::reduce() can handle mixed data types, but you must ensure that the provided operation can manage those types correctly.