Partitioning Custom Data Types

Yes, the partition() function can be used with custom data types in C++. To do this, you need to define a predicate that operates on the members of your custom type.

The predicate determines how the objects are divided into partitions. Consider the following custom type Actor:

1#include <string>
2
3enum class Mood { Friendly, Neutral, Hostile };
4
5class Actor {
6public:
7  Actor(std::string Name, Mood Mood)
8    : Name{Name}, Mood{Mood} {}
9
10  std::string Name;
11  Mood Mood;
12};

To partition a collection of Actor objects such that all friendly actors are separated from the others, you can define a predicate that checks the Mood of each Actor and use it with std::ranges::partition().

Here’s an example:

1#include <algorithm>
2#include <iostream>
3#include <vector>
4
5enum class Mood { Friendly, Neutral, Hostile };
6
Actor Class|Show
7class Actor {/*...*/};
16
17int main() {
18  using enum Mood;
19
20  std::vector<Actor> Actors{
21    {"Angry Goblin", Hostile},
22    {"Helpful Guard", Friendly},
23    {"Surly Goat", Neutral},
24  };
25
26  auto isFriendly = [](const Actor& A) {
27    return A.Mood == Friendly;
28  };
29
30  std::ranges::partition(Actors, isFriendly);
31
32  std::cout << "After partitioning: ";
33  for (const Actor& A : Actors) {
34    std::cout << A.Name << ", ";
35  }
36  std::cout << "\n";
37}

1After partitioning: Helpful Guard, Angry Goblin, Surly Goat,

In this example, the isFriendly predicate checks if an Actor is friendly. The partition() function then rearranges the Actors vector so that all friendly actors are placed at the beginning.

Using partition() with custom data types is a powerful way to organize complex collections based on specific criteria defined by your predicates. Ensure your predicate function is well-defined to avoid unexpected behavior.