Compare two Iterator pointing into a Container Attribute for Equality

compare_iterators

The template compare_iterators is a type used as an attribute customization point. It is invoked by the Karma repetitive generators (such as List (%), Kleene (unary *), Plus (unary +), and Repeat) in order to compare the current iterator (returned either from traits::begin_container or from traits::next_iterator) with the end iterator (returned from traits::end_container) in order to find the end of the element sequence to generate output for.

Module Headers

#include <boost/spirit/home/support/container.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 Iterator, typename Enable>
struct compare_iterators
{
    static bool call(Iterator const& it1, Iterator const& it2);
};

Template parameters

Parameter	Description	Default
`Iterator`	The type, `Iterator` of the iterator to dereference. This is the same as the type returned by the customization point `traits::container_iterator`.	none
`Enable`	Helper template parameter usable to selectively enable or disable certain specializations of `compare_iterators` utilizing SFINAE (i.e. `boost::enable_if` or `boost::disable_if`).	`void`

Notation

Iterator: An iterator type.
it1, it2: Instances of an iterator of type Iterator.
C: A container type whose iterator type is Iterator.

Expression Semantics

Expression	Semantics
`compare_iterators<Iterator>::call(it1, it2)`	Returns whether the iterators `it1` `it2` are to be treated as being equal.

Predefined Specializations

Spirit predefines specializations of this customization point for several types. The following table lists those types together with the types returned by the embedded typedef type:

Template Parameters	Semantics
`Iterator`	The function `call()` returns it1 == it2.
`unused_typeconst*`	The function `call()` always returns false.

When to implement

The customization point compare_iterators needs to be implemented for a specific iterator type whenever the container this iterator belongs to is to be used as an attribute in place of a STL container. It is applicable for generators (Spirit.Karma) only. As a rule of thumb: it has to be implemented whenever a certain iterator type belongs to a container which is to be passed as an attribute to a generator normally exposing a STL container, C and if the container type does not expose the interface of a STL container (i.e. is_container<C>::type would normally return mpl::false_).

Related Attribute Customization Points

If this customization point is implemented, the following other customization points might need to be implemented as well.

Name	When to implement
`traits::is_container`	Needs to be implemented whenever a type is to be used as a container attribute in Karma.
`traits::container_iterator`	Karma: List (`%`), Kleene (unary `*`), Plus (unary `+`), Repeat.
`traits::begin_container`	Karma: List (`%`), Kleene (unary `*`), Plus (unary `+`), Repeat.
`traits::end_container`	Karma: List (`%`), Kleene (unary `*`), Plus (unary `+`), Repeat.
`traits::deref_iterator`	Karma: List (`%`), Kleene (unary `*`), Plus (unary `+`), Repeat.
`traits::next_iterator`	Karma: List (`%`), Kleene (unary `*`), Plus (unary `+`), Repeat.
`traits::compare_iterators`	Karma: List (`%`), Kleene (unary `*`), Plus (unary `+`), Repeat.

Example

For an example of how to use the customization point compare_iterators please see here: use_as_container.