boost_core/doc/nvp.qbk

[/
Copyright 2019 Glen Joseph Fernandes
(glenjofe@gmail.com)

Distributed under the Boost Software License, Version 1.0.
(http://www.boost.org/LICENSE_1_0.txt)
]

[section:nvp nvp]

[section Overview]

The header <boost/core/nvp.hpp> provides the class template `boost::nvp` that
pairs a name (`const char*`) with the address of a value (`T*`). It is the new
implementation of the NVP type previously provided by the Boost Serialization
library. This type now lives in the Core library so that other Boost libraries
can support named value serialization without taking a dependency on the
Serialization library.

[endsect]

[section Examples]

The following snippet shows use in a member serialize function:

```
template<class A>
void serialize(A& archive, unsigned)
{
    archive & boost::make_nvp("x", x_) & boost::make_nvp("y", y_);
}
```

[endsect]

[section Reference]

```
namespace boost {

template<class T>
class nvp {
    nvp(const char* name, T& value) noexcept;

    const char* name() const noexcept;

    T& value() const noexcept;

    const T& const_value() const noexcept;

    template<class A>
    void save(A& archive, unsigned) const;

    template<class A>
    void load(A& archive, unsigned);

    template<class A>
    void serialize(A& archive, unsigned);
};

template<class T>
struct is_nvp;

template<class T>
const nvp<T> make_nvp(const char* name, T& value) noexcept;

} /* boost */
```

[section Constructors]

[variablelist
[[`nvp(const char* name, T& value) noexcept;`]
[Initializes the stored name pointer with `name` and the value pointer with
`addressof(value)`.]]]

[endsect]

[section Members]

[variablelist
[[`const char* name() const noexcept;`]
[Returns the stored name pointer.]]
[[`T& value() const noexcept;`]
[Returns the stored value pointer.]]
[[`const T& const_value() const noexcept;`]
[Returns the stored value pointer.]]
[[`template<class A> void save(A& archive, unsigned) const;`]
[Calls `archive.operator<<(const_value())`.]]
[[`template<class A> void load(A& archive, unsigned);`]
[Calls `archive.operator>>(value())`.]]
[[`template<class A> void serialize(A& archive,
unsigned version);`]
[Calls `save(archive, version)` if `A::is_saving` is a true type,
otherwise `load(archive, version)`.]]]

[endsect]

[section Traits]

[variablelist
[[`template<class T> class is_nvp;`]
[Provides static constant `value` equal to true if `T` is an NVP type,
otherwise false.]]]

[endsect]

[section Functions]

[variablelist
[[`template<class T> const nvp<T> make_nvp(const char* name, T& value)
noexcept;`]
[Returns `nvp<T>(name, value)`.]]]

[endsect]

[endsect]

[section Acknowledgments]

Robert Ramey originally implemented nvp in the Serialization library. Glen
Fernandes implemented this new (but compatible) version in the Core library.

[endsect]

[endsect]