value_ref

`value_ref`

The type used in initializer lists.

Synopsis

Defined in header <boost/json/value_ref.hpp>.

class value_ref;

Member Functions

Name Description

Name	Description
`value_ref` [constructor]	Constructors.

value_ref [constructor]

Constructors.

Description

This type is used in initializer lists for lazy construction of and assignment to the container types value, array, and object. The two types of initializer lists used are:

std::initializer_list< value_ref > for constructing or assigning a value or array, and
std::initializer_list< std::pair< string_view, value_ref > > for constructing or assigning an object.

A value_ref uses reference semantics. Creation of the actual container from the initializer list is lazily deferred until the list is used. This means that the boost::container::pmr::memory_resource used to construct a container can be specified after the point where the initializer list is specified. Also, the usage of this type allows to avoid constructing a value until it’s necessary.

Example

This example demonstrates how a user-defined type containing a JSON value can be constructed from an initializer list:

class my_type
{
    value jv_;

public:
    my_type( std::initializer_list<value_ref> init )
        : jv_(init)
    {
    }
};

value_ref does not take ownership of the objects it was constructed with. If those objects' lifetimes end before the value_ref object is used, you will get undefined behavior. Because of this it is advised against declaring a variable of type std::initializer_list<value_ref> except in function parameter lists.