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Advanced Topics
=====================
Adding new XML parser
-------------------------------------------------
Implementing support for the new XML parser requires creating new specializations for
``svgpp::policy::xml::attribute_iterator`` and ``svgpp::policy::xml::element_iterator``
class templates using one of existing implementations in folder ``include/svgpp/policy/xml`` as a sample.
Understanding following types may cause some difficulties::
template<>
struct attribute_iterator<CustomXMLAttribute>
{
typedef /* ... */ string_type;
typedef /* ... */ attribute_name_type;
typedef /* ... */ attribute_value_type;
typedef /* ... */ saved_value_type;
/* ... */
};
``string_type``
A model of
`Forward Range <http://www.boost.org/doc/libs/1_57_0/libs/range/doc/html/range/concepts/forward_range.html>`_,
with items of some character type (``char``, ``wchar_t``, ``char16_t``, ``char32_t``).
Easy solution is to use ``boost::iterator_range<CharT const *>``.
``attribute_name_type``
Copy constructible type, for which exists method
``string_type attribute_iterator::get_string_range(attribute_name_type const &)``.
Value of ``attribute_name_type`` is used only before ``attribute_iterator``
gets incremented and may become invalid after that.
``attribute_value_type``
Copy constructible type, for which exists method
``string_type attribute_iterator::get_string_range(attribute_value_type const &)``.
Value of ``attribute_value_type`` must be accessible independently of ``attribute_iterator`` state changes.
``saved_value_type``
Copy constructible type, for which exists method
``attribute_value_type attribute_iterator::get_value(saved_value_type const &)``.
Object of this type must as efficiently as possible save attribute value that may be not requested.
For example XML parser provides access to XML attribute like this::
class XmlAttribute
{
public:
std::string getValue() const;
};
In this case ``saved_value_type`` may be defined as ``XmlAttribute const *``, instead of ``std::string``,
to avoid expences of creating and coping string that may not be requested later.
.. include:: value_parser.rst
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