62 lines
1.3 KiB
Plaintext
62 lines
1.3 KiB
Plaintext
|
////
|
||
|
|
Copyright 2022 Peter Dimov
|
||
|
|
Distributed under the Boost Software License, Version 1.0.
|
||
|
|
https://www.boost.org/LICENSE_1_0.txt
|
||
|
|
////
|
||
|
|
|
||
|
|
[#describe]
|
||
|
|
= Hashing User Types with Boost.Describe
|
||
|
|
:idprefix: describe_
|
||
|
|
|
||
|
|
Let's look at our `point` class again:
|
||
|
|
|
||
|
|
[source]
|
||
|
|
----
|
||
|
|
class point
|
||
|
|
{
|
||
|
|
int x;
|
||
|
|
int y;
|
||
|
|
|
||
|
|
public:
|
||
|
|
|
||
|
|
point() : x(0), y(0) {}
|
||
|
|
point(int x, int y) : x(x), y(y) {}
|
||
|
|
};
|
||
|
|
----
|
||
|
|
|
||
|
|
If you're using {cpp}14 or above, a much easier way to add
|
||
|
|
support for `boost::hash` to `point` is by using
|
||
|
|
link:../../../describe/index.html[Boost.Describe] (and
|
||
|
|
get an automatic definition of `operator==` for free):
|
||
|
|
|
||
|
|
[source]
|
||
|
|
----
|
||
|
|
|
||
|
|
#include <boost/describe/class.hpp>
|
||
|
|
#include <boost/describe/operators.hpp>
|
||
|
|
|
||
|
|
class point
|
||
|
|
{
|
||
|
|
int x;
|
||
|
|
int y;
|
||
|
|
|
||
|
|
BOOST_DESCRIBE_CLASS(point, (), (), (), (x, y))
|
||
|
|
|
||
|
|
public:
|
||
|
|
|
||
|
|
point() : x(0), y(0) {}
|
||
|
|
point(int x, int y) : x(x), y(y) {}
|
||
|
|
};
|
||
|
|
|
||
|
|
using boost::describe::operators::operator==;
|
||
|
|
using boost::describe::operators::operator!=;
|
||
|
|
----
|
||
|
|
|
||
|
|
(Full code for this example is at
|
||
|
|
link:../../examples/point2.cpp[examples/point2.cpp].)
|
||
|
|
|
||
|
|
Since the `point` class has been annotated with `BOOST_DESCRIBE_CLASS`,
|
||
|
|
the library can enumerate its members (and base classes) and automatically
|
||
|
|
synthesize the appropriate `hash_value` overload for it, without us needing
|
||
|
|
to do so.
|