Boost.PFR Documentation

Boost.PFR is a C++14 library that provides basic reflection capabilities for aggregate structures. It allows developers to:

• Access structure elements by index (boost::pfr::get<N>).
• Retrieve the number of fields in a type (boost::pfr::tuple_size).
• Serialize structures to a string format (boost::pfr::io).

It achieves this without the need for macros or manual boilerplate, making it highly compatible with existing user-defined aggregate types. It mimics the interface of std::tuple for custom structs.

You can access individual fields of an aggregate structure by their index using boost::pfr::get<N>(instance). This works for any aggregate type without requiring macros or boilerplate code.

#include "boost/pfr.hpp"
#include <string>

struct some_person {
  std::string name;
  unsigned birth_year;
};

some_person val{"Edgar Allan Poe", 1809};

// Accessing elements by index
auto name = boost::pfr::get<0>(val);
auto year = boost::pfr::get<1>(val);

The boost::pfr::io(instance) function allows you to easily serialize an aggregate structure into a string-like format (e.g., for use with std::cout or file streams) without defining custom operator<< overloads for every struct.

#include <iostream>
#include "boost/pfr.hpp"

struct my_struct {
    int i;
    char c;
    double d;
};

int main() {
    my_struct s{100, 'H', 3.141593};
    // Outputs: {100, H, 3.14159}
    std::cout << boost::pfr::io(s) << "\n";
}

To determine how many fields are in an aggregate structure, use boost::pfr::tuple_size<T>::value. This provides std::tuple-like reflection capabilities for user-defined types.

#include "boost/pfr.hpp"

struct my_struct {
    int i;
    char c;
    double d;
};

// Returns the number of fields (3)
std::size_t size = boost::pfr::tuple_size<my_struct>::value;