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<body>
<p>If you want to use the json methods <code>is&lt;T&gt;</code>, <code>as&lt;T&gt;</code>, <code>add</code>, <code>set</code> and <code>operator=</code> to access or modify with a new type, you need to show json how to interact with that type, by extending <code>json_type_traits</code> in the <code>jsoncons</code> namespace.</p>

<p>For example, by including the header file <code>jsoncons_ext/boost/type_extensions.hpp</code>, you can access and modify <code>json</code> values with <code>boost::gregorian</code> dates.</p>

<div class="highlight highlight-source-c++"><pre>    #<span class="pl-k">include</span> <span class="pl-s"><span class="pl-pds">"</span>jsoncons/json.hpp<span class="pl-pds">"</span></span>
    #<span class="pl-k">include</span> <span class="pl-s"><span class="pl-pds">"</span>jsoncons_ext/boost/type_extensions.hpp<span class="pl-pds">"</span></span>

    <span class="pl-k">namespace</span> <span class="pl-en">my</span>
    {
        <span class="pl-k">using</span> jsoncons::json;
        <span class="pl-k">using</span> boost::gregorian::date;

        json deal;
        deal[<span class="pl-s"><span class="pl-pds">"</span>Maturity<span class="pl-pds">"</span></span>] = date(<span class="pl-c1">2014</span>,<span class="pl-c1">10</span>,<span class="pl-c1">14</span>);

        json observation_dates = json::array();
        observation_dates.add(date(<span class="pl-c1">2014</span>,<span class="pl-c1">2</span>,<span class="pl-c1">14</span>));
        observation_dates.add(date(<span class="pl-c1">2014</span>,<span class="pl-c1">2</span>,<span class="pl-c1">21</span>));

        deal[<span class="pl-s"><span class="pl-pds">"</span>ObservationDates<span class="pl-pds">"</span></span>] = std::move(observation_dates);

        date maturity = deal[<span class="pl-s"><span class="pl-pds">"</span>Maturity<span class="pl-pds">"</span></span>].as&lt;date&gt;();
        std::cout &lt;&lt; <span class="pl-s"><span class="pl-pds">"</span>Maturity: <span class="pl-pds">"</span></span> &lt;&lt; maturity &lt;&lt; std::endl &lt;&lt; std::endl;

        std::cout &lt;&lt; <span class="pl-s"><span class="pl-pds">"</span>Observation dates: <span class="pl-pds">"</span></span> &lt;&lt; std::endl &lt;&lt; std::endl;
        json::array_iterator it = deal[<span class="pl-s"><span class="pl-pds">"</span>ObservationDates<span class="pl-pds">"</span></span>].elements().begin();
        json::array_iterator end = deal[<span class="pl-s"><span class="pl-pds">"</span>ObservationDates<span class="pl-pds">"</span></span>].end_elements();

        <span class="pl-k">while</span> (it != end)
        {
            date d = it-&gt;as&lt;date&gt;();
            std::cout &lt;&lt; d &lt;&lt; std::endl;
            ++it;
        }
        std::cout &lt;&lt; std::endl;

        std::cout &lt;&lt; pretty_print(deal) &lt;&lt; std::endl;
    }</pre></div>

<p>The output is</p>

<pre><code>Maturity: 2014-Oct-14

Observation dates:

2014-Feb-14
2014-Feb-21
</code></pre>

<div class="highlight highlight-source-json"><pre>    {
        <span class="pl-s"><span class="pl-pds">"</span>Maturity<span class="pl-pds">"</span></span>:<span class="pl-s"><span class="pl-pds">"</span>2014-10-14<span class="pl-pds">"</span></span>,
        <span class="pl-s"><span class="pl-pds">"</span>ObservationDates<span class="pl-pds">"</span></span>:
        [<span class="pl-s"><span class="pl-pds">"</span>2014-02-14<span class="pl-pds">"</span></span>,<span class="pl-s"><span class="pl-pds">"</span>2014-02-21<span class="pl-pds">"</span></span>]
    }</pre></div>

<p>You can look in the header file <code>jsoncons_ext/boost/type_extensions.hpp</code><br>
to see how the specialization of <code>json_type_traits</code> that supports<br>
the conversions works. In this implementation the <code>boost</code> date values are stored in the <code>json</code> values as strings.</p>

<div class="highlight highlight-source-c++"><pre>    <span class="pl-k">namespace</span> <span class="pl-en">jsoncons</span> 
    {
        <span class="pl-k">template </span>&lt;<span class="pl-k">typename</span> JsonT&gt;
        <span class="pl-k">class</span> <span class="pl-en">json_type_traits</span>&lt;JsonT,boost::gregorian::date&gt;
        {
        <span class="pl-k">public:</span>
            <span class="pl-k">static</span> <span class="pl-k">bool</span> <span class="pl-en">is</span>(<span class="pl-k">const</span> JsonT&amp; val) noexcept
            {
                <span class="pl-k">if</span> (!val.<span class="pl-c1">is_string</span>())
                {
                    <span class="pl-k">return</span> <span class="pl-c1">false</span>;
                }
                std::string s = val.<span class="pl-smi">template</span> as&lt;std::string&gt;();
                <span class="pl-k">try</span>
                {
                    <span class="pl-c1">boost::gregorian::date_from_iso_string</span>(s);
                    <span class="pl-k">return</span> <span class="pl-c1">true</span>;
                }
                <span class="pl-k">catch</span> (...)
                {
                    <span class="pl-k">return</span> <span class="pl-c1">false</span>;
                }
            }

            <span class="pl-k">static</span> boost::gregorian::date <span class="pl-en">as</span>(<span class="pl-k">const</span> JsonT&amp; val)
            {
                std::string s = val.<span class="pl-smi">template</span> as&lt;std::string&gt;();
                <span class="pl-k">return</span> <span class="pl-c1">boost::gregorian::from_simple_string</span>(s);
            }

            <span class="pl-k">static</span> <span class="pl-k">void</span> <span class="pl-en">assign</span>(JsonT&amp; lhs, boost::gregorian::date val)
            {
                lhs = <span class="pl-c1">to_iso_extended_string</span>(val);
            }
        };
    }</pre></div>
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