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                <li class="toctree-l3"><a href="#stack-interaction">Stack interaction</a></li>
                
                    <li><a class="toctree-l4" href="#extending-supported-types">Extending supported types</a></li>
                
                    <li><a class="toctree-l4" href="#pushing-c-values">Pushing C++ values</a></li>
                
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                <h1 id="stack-interaction">Stack interaction</h1>
<p>A fundamental aspect of this is the abstract template <a href="../reference/structluwra_1_1Value.html">Value</a>. Every type which can be
pushed onto or read from the stack has a specialization of it. Useful implementations are provided
out of the box:</p>
<table>
<thead>
<tr>
<th>C++ type</th>
<th>Pushable</th>
<th>Readable</th>
<th>Lua type</th>
</tr>
</thead>
<tbody>
<tr>
<td>bool</td>
<td>yes</td>
<td>yes</td>
<td>boolean</td>
</tr>
<tr>
<td>signed char</td>
<td>yes</td>
<td>yes</td>
<td>number (integer since 5.3)</td>
</tr>
<tr>
<td>signed short</td>
<td>yes</td>
<td>yes</td>
<td>number (integer since 5.3)</td>
</tr>
<tr>
<td>signed int</td>
<td>yes</td>
<td>yes</td>
<td>number (integer since 5.3)</td>
</tr>
<tr>
<td>signed long int</td>
<td>yes</td>
<td>yes</td>
<td>number (integer since 5.3)</td>
</tr>
<tr>
<td>signed long long int</td>
<td>yes</td>
<td>yes</td>
<td>number (integer since 5.3)</td>
</tr>
<tr>
<td>unsigned char</td>
<td>yes</td>
<td>yes</td>
<td>number (integer since 5.3)</td>
</tr>
<tr>
<td>unsigned short</td>
<td>yes</td>
<td>yes</td>
<td>number (integer since 5.3)</td>
</tr>
<tr>
<td>unsigned int</td>
<td>yes</td>
<td>yes</td>
<td>number (integer since 5.3)</td>
</tr>
<tr>
<td>unsigned long int</td>
<td>yes</td>
<td>yes</td>
<td>number (integer since 5.3)</td>
</tr>
<tr>
<td>unsigned long long int</td>
<td>yes</td>
<td>yes</td>
<td>number (integer since 5.3)</td>
</tr>
<tr>
<td>float</td>
<td>yes</td>
<td>yes</td>
<td>number</td>
</tr>
<tr>
<td>double</td>
<td>yes</td>
<td>yes</td>
<td>number</td>
</tr>
<tr>
<td>long double</td>
<td>yes</td>
<td>yes</td>
<td>number</td>
</tr>
<tr>
<td>const char*</td>
<td>yes</td>
<td>yes</td>
<td>string</td>
</tr>
<tr>
<td>std::string</td>
<td>yes</td>
<td>yes</td>
<td>string</td>
</tr>
<tr>
<td>std::nullptr_t</td>
<td>yes</td>
<td>yes</td>
<td>nil</td>
</tr>
<tr>
<td>std::tuple&lt;T...&gt;</td>
<td>yes</td>
<td>no</td>
<td><em>depends on the tuple contents</em></td>
</tr>
<tr>
<td>std::vector&lt;T&gt;</td>
<td>yes</td>
<td>yes</td>
<td>table</td>
</tr>
<tr>
<td>std::list&lt;T&gt;</td>
<td>yes</td>
<td>yes</td>
<td>table</td>
</tr>
<tr>
<td>std::map&lt;K, V&gt;</td>
<td>yes</td>
<td>yes</td>
<td>table</td>
</tr>
<tr>
<td><a href="http://www.lua.org/manual/5.3/manual.html#lua_CFunction">lua_CFunction</a></td>
<td>yes</td>
<td>no</td>
<td>function, table or userdata</td>
</tr>
<tr>
<td><a href="../reference/structluwra_1_1NativeFunction_3_01R_07A_8_8_8_08_4.html">NativeFunction</a></td>
<td>yes</td>
<td>yes</td>
<td>function</td>
</tr>
<tr>
<td><a href="../reference/structluwra_1_1Table.html">Table</a></td>
<td>yes</td>
<td>yes</td>
<td>table</td>
</tr>
</tbody>
</table>
<p><strong>Note:</strong> Some numeric types have a different size than their matching Lua type - they will be
truncated during push or read operations.</p>
<h2 id="extending-supported-types">Extending supported types</h2>
<p>If you are missing a type that cannot be used as a <a href="../user-types">user type</a>, you can add a
specialization of <a href="../reference/structluwra_1_1Value.html">Value</a>. All you need to do is modify the following snippet for your
type <code>T</code>.</p>
<pre><code class="c++">namespace luwra {
    template &lt;&gt;
    struct Value&lt;T&gt; {
        static inline
        T read(State* state, int index) {
            return /* Return the instance of T that you have read at the given index */;
        }

        static inline
        size_t push(State* state, const T&amp; value) {
            // Push the given value on top of the stack
            return /* Return how many values you have pushed onto the stack */;
        }
    };
}
</code></pre>

<h2 id="pushing-c-values">Pushing C++ values</h2>
<p>When pushing values onto the stack you can either use <a href="../reference/structluwra_1_1Value.html#aa376d68285606c206562b822e8187384">Value&lt;T&gt;::push</a> or
the more convenient <a href="../reference/namespaceluwra.html#ae8e7eab11fc2cf3f258ffd81571066fa">push</a>.</p>
<pre><code class="c++">// Push an integer
luwra::push(lua, 1338);

// Push a number
luwra::push(lua, 13.37);

// Push a boolean
luwra::push(lua, false);

// Push a string
luwra::push(lua, &quot;Hello World&quot;);

// Push a table
luwra::push(lua, luwra::MemberMap {
    {&quot;one&quot;, 1},
    {1, &quot;one&quot;},
    {&quot;nested&quot;, luwra::MemberMap {
        {&quot;more&quot;, &quot;fields&quot;}
    }}
});
</code></pre>

<p><strong>Note:</strong> <a href="../reference/namespaceluwra.html#a2e12e40b973f0f56cb9a1dc91bef882a">luwra::MemberMap</a> is an alias for
<code>std:map&lt;luwra::Pushable, luwra::Pushable&gt;</code>. Its keys and values are constructible using any
pushable type.</p>
<p>This produces the following stack layout:</p>
<table>
<thead>
<tr>
<th>Absolute Position</th>
<th>Relative Position</th>
<th>Value</th>
</tr>
</thead>
<tbody>
<tr>
<td>1</td>
<td>-5</td>
<td><code>1338</code></td>
</tr>
<tr>
<td>2</td>
<td>-4</td>
<td><code>13.37</code></td>
</tr>
<tr>
<td>3</td>
<td>-3</td>
<td><code>false</code></td>
</tr>
<tr>
<td>4</td>
<td>-2</td>
<td><code>"Hello World"</code></td>
</tr>
<tr>
<td>5</td>
<td>-1</td>
<td><code>{one = 1, [1] = "one", nested = {more = "fields"}}</code></td>
</tr>
</tbody>
</table>
<p>It is possible to provide a template parameter to <code>push</code> to enforce pushing a specific type.
In most cases you are probably better off by letting the compiler infer the template parameter.</p>
<h2 id="reading-lua-values">Reading Lua values</h2>
<p>Simple retrieval of Lua values is done using <a href="../reference/namespaceluwra.html#a4fe4e574680cf54a0f8d958740eb90ab">read&lt;T&gt;</a>. Consider the stack layout
from the previous example. This is how you would retrieve a value from the stack.</p>
<pre><code class="c++">// Retrieve the integer at position 1
int value = luwra::read&lt;int&gt;(lua, 1);

// Similiar with a relative index
int value = luwra::read&lt;int&gt;(lua, -5);
</code></pre>

<h2 id="read-and-type-errors">Read and type errors</h2>
<p>What happens when a value mismatches the expected type or cannot be converted to it? Most
<a href="../reference/structluwra_1_1Value.html">Value</a> specializations use Lua's <code>luaL_check*</code> functions to retrieve the values from
the stack. This means that no exceptions will be thrown - instead the error handling is delegated to
the Lua VM. Have a look at the <a href="http://www.lua.org/manual/5.3/manual.html#4.6">error handling documentation</a> for more
information.</p>
              
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