////
Copyright 2020 Peter Dimov
Distributed under the Boost Software License, Version 1.0.
https://www.boost.org/LICENSE_1_0.txt
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[#owner_hash]
# owner_hash
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:toc-title:
:idprefix: owner_hash_to_
## Description
`owner_hash<T>` is a helper function object that takes a smart pointer `p`
and returns `p.owner_hash_value()`. It's useful for creating unordered
containers of `shared_ptr` that use ownership-based equality, instead of
the default pointer value equality. (It can be used with `weak_ptr` too,
but there's no need, because `boost::hash` and `std::hash` for `weak_ptr`
already use ownership-based equality.)
## Example
```
std::unordered_set< boost::shared_ptr<void>,
boost::owner_hash< boost::shared_ptr<void> >,
boost::owner_equal_to< boost::shared_ptr<void> > > set;
```
## Synopsis
`owner_hash` is defined in `<boost/smart_ptr/owner_hash.hpp>`.
```
namespace boost {
template<class T> struct owner_hash
{
typedef std::size_t result_type;
typedef T argument_type;
std::size_t operator()( T const & p ) const noexcept;
};
}
```
## Members
```
std::size_t operator()( T const & p ) const noexcept;
```
[none]
* {blank}
+
Returns::
`p.owner_hash_value()`.