Store an Attribute Value into a Container after a Parser Produced a Value (Qi)

assign_to_container_from_value

The template assign_to_container_from_value is a type used as an attribute customization point. It is invoked by all primitive Qi parsers in order to store a parsed attribute value into the attribute instance provided by the user, if this attribute is a container type (is_container<T>::type evaluates to mpl::true_, where T is the attribute type).

Module Headers

#include <boost/spirit/home/qi/detail/assign_to.hpp>

Also, see Include Structure.

	Note
	This header file does not need to be included directly by any user program as it is normally included by other Spirit header files relying on its content.

Namespace

Name
`boost::spirit::traits`

Synopsis

template <typename Attrib, typename T, typename Enable>
struct assign_to_container_from_value
{
    static void call(T const& val, Attrib& attr);
};

Template parameters

Parameter	Description	Default
`Attrib`	The type, `Attrib` is the type of the attribute as passed in by the user. This type is a container type (`is_container<Attrib>::type` evaluates to `mpl::true_`).	none
`T`	The type, `T` is the type of the attribute instance as produced by the parser.	none
`Enable`	Helper template parameter usable to selectively enable or disable certain specializations of `assign_to_container_from_value` utilizing SFINAE (i.e. `boost::enable_if` or `boost::disable_if`).	`void`

Notation

Attrib: A type to be used as the target to store the attribute value in. This type is guaranteed to be a container type (is_container<Attrib>::type evaluates to mpl::true_).
attr: An attribute instance of type Attrib.
T: A type as produced by the parser. The parser temporarily stores its parsed values using this type.
t: An attribute instance of type T.

Expression Semantics

Expression	Semantics
assign_to_container_from_value<Attrib, T>::call(t, attr)	Add the value `t` to the container attribute `attr`.

Expression

Semantics

assign_to_container_from_value<Attrib, T>::call(t, attr)

Add the value t to the container attribute attr.

Predefined Specializations

Template Parameters	Semantics
`Attrib`, `T`	Add the argument `t` to `attr`.
`unused_type`, `T`	Do nothing.

When to implement

The customization point assign_to_container_from_value needs to be implemented for a specific type whenever the default implementation as shown above is not applicable. Examples for this could be that the type Attrib is not copy constructible.