In C++ 20 we are able let the compiler automatically generate the implementation for operator==
for us like this (and all the other default comparasions too, but I'm just interested in operator==
here):
#include <compare>
struct Point {
int x;
int y;
bool operator==(const Point&) const = default;
};
Is there a way to archieve the same (automatically generate operator==
) but in C++17?
Since libraries are an okay solution I had a look at boost/operators. Would the following be the equivalent as the above?
#include <boost/operators.hpp>
struct Point : boost<equality_comparable<Point, Point>> {
int x;
int y;
bool operator==(const Point&) const; // will this get auto-generated too and do the same as above?
};
Only for aggregates (a slightly widened set around POD (trivial+standard layout) types).
Using PFR you can opt in using a macro:
Boost.PFR adds the following out-of-the-box functionality for aggregate initializable structures:
- comparison functions
- heterogeneous comparators
- hash
- IO streaming
- access to members by index
- member type retrieval
- methods for cooperation with std::tuple
- methods to visit each field of the structure
Example using BOOST_PFR_FUNCTIONS_FOR
:
Defines comparison and stream operators for T along with hash_value function.
See Also : 'Three ways of getting operators' for other ways to define operators and more details.
struct Point { int x, y; };
#include <boost/pfr.hpp>
BOOST_PFR_FUNCTIONS_FOR(Point)
#include <iostream>
#include <vector>
#include <set>
int main() {
std::vector pv { Point{1,2}, {2,1}, {-3,4}, {1,4/2}, {-3,-4} };
for(auto& p : pv) std::cout << p << " ";
std::cout << "\n";
std::set ps(begin(pv), end(pv));
for(auto& p : ps) std::cout << p << " ";
std::cout << "\n";
}
Prints
{1, 2} {2, 1} {-3, 4} {1, 2} {-3, -4}
{-3, -4} {-3, 4} {1, 2} {2, 1}
Using strictly c++14 (specifying vector<Point>
and set<Point>
template arguments).