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  27 <a name="boost.units.quantity_BOOS_idp770255952"></a><div class="titlepage"></div>
  28 <div class="refnamediv">
  29 <h2><span class="refentrytitle">Class template quantity&lt;BOOST_UNITS_DIMENSIONLESS_UNIT(System), Y&gt;</span></h2>
  30 <p>boost::units::quantity&lt;BOOST_UNITS_DIMENSIONLESS_UNIT(System), Y&gt;</p>
  31 </div>
  32 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
  33 <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../boost_units/Reference.html#header.boost.units.quantity_hpp" title="Header &lt;boost/units/quantity.hpp&gt;">boost/units/quantity.hpp</a>&gt;
  34
  35 </span><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> System<span class="special">,</span> <span class="keyword">typename</span> Y<span class="special">&gt;</span>
  36 <span class="keyword">class</span> <a class="link" href="quantity_BOOS_idp770255952.html" title="Class template quantity&lt;BOOST_UNITS_DIMENSIONLESS_UNIT(System), Y&gt;">quantity</a><span class="special">&lt;</span><span class="identifier">BOOST_UNITS_DIMENSIONLESS_UNIT</span><span class="special">(</span><span class="identifier">System</span><span class="special">)</span><span class="special">,</span> <span class="identifier">Y</span><span class="special">&gt;</span> <span class="special">{</span>
  37 <span class="keyword">public</span><span class="special">:</span>
  38   <span class="comment">// types</span>
  39   <span class="keyword">typedef</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <a class="link" href="unit.html" title="Class template unit">unit</a><span class="special">&lt;</span> <a class="link" href="dimensionless_type.html" title="Struct dimensionless_type">dimensionless_type</a><span class="special">,</span> <span class="identifier">System</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">Y</span> <span class="special">&gt;</span> <a name="boost.units.quantity_BOOS_idp770255952.this_type"></a><span class="identifier">this_type</span><span class="special">;</span>
  40   <span class="keyword">typedef</span> <span class="identifier">Y</span>                                                 <a name="boost.units.quantity_BOOS_idp770255952.value_type"></a><span class="identifier">value_type</span><span class="special">;</span>
  41   <span class="keyword">typedef</span> <span class="identifier">System</span>                                            <a name="boost.units.quantity_BOOS_idp770255952.system_type"></a><span class="identifier">system_type</span><span class="special">;</span>
  42   <span class="keyword">typedef</span> <a class="link" href="dimensionless_type.html" title="Struct dimensionless_type">dimensionless_type</a>                                <a name="boost.units.quantity_BOOS_idp770255952.dimension_type"></a><span class="identifier">dimension_type</span><span class="special">;</span>
  43   <span class="keyword">typedef</span> <a class="link" href="unit.html" title="Class template unit">unit</a><span class="special">&lt;</span> <span class="identifier">dimension_type</span><span class="special">,</span> <span class="identifier">system_type</span> <span class="special">&gt;</span>               <a name="boost.units.quantity_BOOS_idp770255952.unit_type"></a><span class="identifier">unit_type</span><span class="special">;</span>
  44
  45   <span class="comment">// <a class="link" href="quantity_BOOS_idp770255952.html#boost.units.quantity_BOOS_idp770255952construct-copy-destruct">construct/copy/destruct</a></span>
  46   <a class="link" href="quantity_BOOS_idp770255952.html#idp770277248-bb"><span class="identifier">quantity</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
  47   <a class="link" href="quantity_BOOS_idp770255952.html#idp770277536-bb"><span class="identifier">quantity</span></a><span class="special">(</span><span class="identifier">value_type</span><span class="special">)</span><span class="special">;</span>
  48   <a class="link" href="quantity_BOOS_idp770255952.html#idp770279248-bb"><span class="identifier">quantity</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">this_type</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  49   <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> YY<span class="special">&gt;</span>
  50     <a class="link" href="quantity_BOOS_idp770255952.html#idp770281488-bb"><span class="identifier">quantity</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <a class="link" href="unit.html" title="Class template unit">unit</a><span class="special">&lt;</span> <span class="identifier">dimension_type</span><span class="special">,</span> <span class="identifier">system_type</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">YY</span> <span class="special">&gt;</span> <span class="special">&amp;</span><span class="special">,</span>
  51              <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span>
  52   <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> YY<span class="special">&gt;</span>
  53     <span class="keyword">explicit</span> <a class="link" href="quantity_BOOS_idp770255952.html#idp770285696-bb"><span class="identifier">quantity</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <a class="link" href="unit.html" title="Class template unit">unit</a><span class="special">&lt;</span> <span class="identifier">dimension_type</span><span class="special">,</span> <span class="identifier">system_type</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">YY</span> <span class="special">&gt;</span> <span class="special">&amp;</span><span class="special">,</span>
  54                       <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span>
  55   <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> System2<span class="special">,</span> <span class="keyword">typename</span> Y2<span class="special">&gt;</span>
  56     <a class="link" href="quantity_BOOS_idp770255952.html#idp770293568-bb"><span class="identifier">quantity</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <a class="link" href="unit.html" title="Class template unit">unit</a><span class="special">&lt;</span> <a class="link" href="dimensionless_type.html" title="Struct dimensionless_type">dimensionless_type</a><span class="special">,</span> <span class="identifier">System2</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">Y2</span> <span class="special">&gt;</span> <span class="special">&amp;</span><span class="special">,</span>
  57              <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span>
  58   <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> System2<span class="special">,</span> <span class="keyword">typename</span> Y2<span class="special">&gt;</span>
  59     <span class="keyword">explicit</span> <a class="link" href="quantity_BOOS_idp770255952.html#idp770300944-bb"><span class="identifier">quantity</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <a class="link" href="unit.html" title="Class template unit">unit</a><span class="special">&lt;</span> <a class="link" href="dimensionless_type.html" title="Struct dimensionless_type">dimensionless_type</a><span class="special">,</span> <span class="identifier">System2</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">Y2</span> <span class="special">&gt;</span> <span class="special">&amp;</span><span class="special">,</span>
  60                       <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span>
  61   <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> System2<span class="special">,</span> <span class="keyword">typename</span> Y2<span class="special">&gt;</span>
  62     <span class="keyword">explicit</span> <a class="link" href="quantity_BOOS_idp770255952.html#idp770308592-bb"><span class="identifier">quantity</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <a class="link" href="unit.html" title="Class template unit">unit</a><span class="special">&lt;</span> <a class="link" href="dimensionless_type.html" title="Struct dimensionless_type">dimensionless_type</a><span class="special">,</span> <span class="identifier">System2</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">Y2</span> <span class="special">&gt;</span> <span class="special">&amp;</span><span class="special">,</span>
  63                       <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span>
  64   <span class="identifier">this_type</span> <span class="special">&amp;</span> <a class="link" href="quantity_BOOS_idp770255952.html#idp770280224-bb"><span class="keyword">operator</span><span class="special">=</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">this_type</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  65   <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> YY<span class="special">&gt;</span>
  66     <span class="identifier">this_type</span> <span class="special">&amp;</span> <a class="link" href="quantity_BOOS_idp770255952.html#idp770290176-bb"><span class="keyword">operator</span><span class="special">=</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <a class="link" href="unit.html" title="Class template unit">unit</a><span class="special">&lt;</span> <span class="identifier">dimension_type</span><span class="special">,</span> <span class="identifier">system_type</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">YY</span> <span class="special">&gt;</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  67   <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> System2<span class="special">&gt;</span>
  68     <span class="identifier">this_type</span> <span class="special">&amp;</span> <a class="link" href="quantity_BOOS_idp770255952.html#idp770314192-bb"><span class="keyword">operator</span><span class="special">=</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <span class="identifier">BOOST_UNITS_DIMENSIONLESS_UNIT</span><span class="special">(</span><span class="identifier">System2</span><span class="special">)</span><span class="special">,</span> <span class="identifier">Y</span> <span class="special">&gt;</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  69
  70   <span class="comment">// <a class="link" href="quantity_BOOS_idp770255952.html#idp770265392-bb">public member functions</a></span>
  71   <a class="link" href="quantity_BOOS_idp770255952.html#idp770265952-bb"><span class="keyword">operator</span> <span class="identifier">value_type</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  72   <span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&amp;</span> <a class="link" href="quantity_BOOS_idp770255952.html#idp770267808-bb"><span class="identifier">value</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  73   <span class="identifier">this_type</span> <span class="special">&amp;</span> <a class="link" href="quantity_BOOS_idp770255952.html#idp770269744-bb"><span class="keyword">operator</span><span class="special">+=</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">this_type</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  74   <span class="identifier">this_type</span> <span class="special">&amp;</span> <a class="link" href="quantity_BOOS_idp770255952.html#idp770271680-bb"><span class="keyword">operator</span><span class="special">-=</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">this_type</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  75   <span class="identifier">this_type</span> <span class="special">&amp;</span> <a class="link" href="quantity_BOOS_idp770255952.html#idp770273616-bb"><span class="keyword">operator</span><span class="special">*=</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  76   <span class="identifier">this_type</span> <span class="special">&amp;</span> <a class="link" href="quantity_BOOS_idp770255952.html#idp770275552-bb"><span class="keyword">operator</span><span class="special">/=</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  77
  78   <span class="comment">// <a class="link" href="quantity_BOOS_idp770255952.html#idp770317120-bb">public static functions</a></span>
  79   <span class="keyword">static</span> <span class="identifier">this_type</span> <a class="link" href="quantity_BOOS_idp770255952.html#idp770317680-bb"><span class="identifier">from_value</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  80 <span class="special">}</span><span class="special">;</span></pre></div>
  81 <div class="refsect1">
  82 <a name="idp588413360"></a><h2>Description</h2>
  83 <p>Specialization for dimensionless quantities. Implicit conversions between unit systems are allowed because all dimensionless quantities are equivalent. Implicit construction and assignment from and conversion to <code class="computeroutput">value_type</code> is also allowed. </p>
  84 <div class="refsect2">
  85 <a name="idp588414976"></a><h3>
  86 <a name="boost.units.quantity_BOOS_idp770255952construct-copy-destruct"></a><code class="computeroutput">quantity</code>
  87         public
  88        construct/copy/destruct</h3>
  89 <div class="orderedlist"><ol class="orderedlist" type="1">
  90 <li class="listitem"><pre class="literallayout"><a name="idp770277248-bb"></a><span class="identifier">quantity</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre></li>
  91 <li class="listitem">
  92 <pre class="literallayout"><a name="idp770277536-bb"></a><span class="identifier">quantity</span><span class="special">(</span><span class="identifier">value_type</span> val<span class="special">)</span><span class="special">;</span></pre>construction from raw <code class="computeroutput">value_type</code> is allowed </li>
  93 <li class="listitem"><pre class="literallayout"><a name="idp770279248-bb"></a><span class="identifier">quantity</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">this_type</span> <span class="special">&amp;</span> source<span class="special">)</span><span class="special">;</span></pre></li>
  94 <li class="listitem">
  95 <pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> YY<span class="special">&gt;</span>
  96   <a name="idp770281488-bb"></a><span class="identifier">quantity</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <a class="link" href="unit.html" title="Class template unit">unit</a><span class="special">&lt;</span> <span class="identifier">dimension_type</span><span class="special">,</span> <span class="identifier">system_type</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">YY</span> <span class="special">&gt;</span> <span class="special">&amp;</span> source<span class="special">,</span>
  97            <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span></pre>implicit conversion between value types is allowed if allowed for value types themselves </li>
  98 <li class="listitem">
  99 <pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> YY<span class="special">&gt;</span>
 100   <span class="keyword">explicit</span> <a name="idp770285696-bb"></a><span class="identifier">quantity</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <a class="link" href="unit.html" title="Class template unit">unit</a><span class="special">&lt;</span> <span class="identifier">dimension_type</span><span class="special">,</span> <span class="identifier">system_type</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">YY</span> <span class="special">&gt;</span> <span class="special">&amp;</span> source<span class="special">,</span>
 101                     <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span></pre>implicit conversion between value types is not allowed if not allowed for value types themselves </li>
 102 <li class="listitem">
 103 <pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> System2<span class="special">,</span> <span class="keyword">typename</span> Y2<span class="special">&gt;</span>
 104   <a name="idp770293568-bb"></a><span class="identifier">quantity</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <a class="link" href="unit.html" title="Class template unit">unit</a><span class="special">&lt;</span> <a class="link" href="dimensionless_type.html" title="Struct dimensionless_type">dimensionless_type</a><span class="special">,</span> <span class="identifier">System2</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">Y2</span> <span class="special">&gt;</span> <span class="special">&amp;</span> source<span class="special">,</span>
 105            <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span></pre>implicit conversion between different unit systems is allowed </li>
 106 <li class="listitem">
 107 <pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> System2<span class="special">,</span> <span class="keyword">typename</span> Y2<span class="special">&gt;</span>
 108   <span class="keyword">explicit</span> <a name="idp770300944-bb"></a><span class="identifier">quantity</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <a class="link" href="unit.html" title="Class template unit">unit</a><span class="special">&lt;</span> <a class="link" href="dimensionless_type.html" title="Struct dimensionless_type">dimensionless_type</a><span class="special">,</span> <span class="identifier">System2</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">Y2</span> <span class="special">&gt;</span> <span class="special">&amp;</span> source<span class="special">,</span>
 109                     <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span></pre>implicit conversion between different unit systems is allowed </li>
 110 <li class="listitem">
 111 <pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> System2<span class="special">,</span> <span class="keyword">typename</span> Y2<span class="special">&gt;</span>
 112   <span class="keyword">explicit</span> <a name="idp770308592-bb"></a><span class="identifier">quantity</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <a class="link" href="unit.html" title="Class template unit">unit</a><span class="special">&lt;</span> <a class="link" href="dimensionless_type.html" title="Struct dimensionless_type">dimensionless_type</a><span class="special">,</span> <span class="identifier">System2</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">Y2</span> <span class="special">&gt;</span> <span class="special">&amp;</span> source<span class="special">,</span>
 113                     <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span></pre>
 114 <p>conversion between different unit systems is explicit when the units are not equivalent. </p>
 115 </li>
 116 <li class="listitem"><pre class="literallayout"><span class="identifier">this_type</span> <span class="special">&amp;</span> <a name="idp770280224-bb"></a><span class="keyword">operator</span><span class="special">=</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">this_type</span> <span class="special">&amp;</span> source<span class="special">)</span><span class="special">;</span></pre></li>
 117 <li class="listitem">
 118 <pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> YY<span class="special">&gt;</span>
 119   <span class="identifier">this_type</span> <span class="special">&amp;</span> <a name="idp770290176-bb"></a><span class="keyword">operator</span><span class="special">=</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <a class="link" href="unit.html" title="Class template unit">unit</a><span class="special">&lt;</span> <span class="identifier">dimension_type</span><span class="special">,</span> <span class="identifier">system_type</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">YY</span> <span class="special">&gt;</span> <span class="special">&amp;</span> source<span class="special">)</span><span class="special">;</span></pre>implicit assignment between value types is allowed if allowed for value types themselves </li>
 120 <li class="listitem">
 121 <pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> System2<span class="special">&gt;</span>
 122   <span class="identifier">this_type</span> <span class="special">&amp;</span> <a name="idp770314192-bb"></a><span class="keyword">operator</span><span class="special">=</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="quantity.html" title="Class template quantity">quantity</a><span class="special">&lt;</span> <span class="identifier">BOOST_UNITS_DIMENSIONLESS_UNIT</span><span class="special">(</span><span class="identifier">System2</span><span class="special">)</span><span class="special">,</span> <span class="identifier">Y</span> <span class="special">&gt;</span> <span class="special">&amp;</span> source<span class="special">)</span><span class="special">;</span></pre>implicit assignment between different unit systems is allowed </li>
 123 </ol></div>
 124 </div>
 125 <div class="refsect2">
 126 <a name="idp588576896"></a><h3>
 127 <a name="idp770265392-bb"></a><code class="computeroutput">quantity</code> public member functions</h3>
 128 <div class="orderedlist"><ol class="orderedlist" type="1">
 129 <li class="listitem">
 130 <pre class="literallayout"><a name="idp770265952-bb"></a><span class="keyword">operator</span> <span class="identifier">value_type</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>implicit conversion to <code class="computeroutput">value_type</code> is allowed </li>
 131 <li class="listitem">
 132 <pre class="literallayout"><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&amp;</span> <a name="idp770267808-bb"></a><span class="identifier">value</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>constant accessor to value <p>can add a quantity of the same type if add_typeof_helper&lt;value_type,value_type&gt;::type is convertible to value_type </p>
 133 </li>
 134 <li class="listitem">
 135 <pre class="literallayout"><span class="identifier">this_type</span> <span class="special">&amp;</span> <a name="idp770269744-bb"></a><span class="keyword">operator</span><span class="special">+=</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">this_type</span> <span class="special">&amp;</span> source<span class="special">)</span><span class="special">;</span></pre>can subtract a quantity of the same type if subtract_typeof_helper&lt;value_type,value_type&gt;::type is convertible to value_type </li>
 136 <li class="listitem">
 137 <pre class="literallayout"><span class="identifier">this_type</span> <span class="special">&amp;</span> <a name="idp770271680-bb"></a><span class="keyword">operator</span><span class="special">-=</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">this_type</span> <span class="special">&amp;</span> source<span class="special">)</span><span class="special">;</span></pre>can multiply a quantity by a scalar value_type if multiply_typeof_helper&lt;value_type,value_type&gt;::type is convertible to value_type </li>
 138 <li class="listitem">
 139 <pre class="literallayout"><span class="identifier">this_type</span> <span class="special">&amp;</span> <a name="idp770273616-bb"></a><span class="keyword">operator</span><span class="special">*=</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&amp;</span> val<span class="special">)</span><span class="special">;</span></pre>can divide a quantity by a scalar value_type if divide_typeof_helper&lt;value_type,value_type&gt;::type is convertible to value_type </li>
 140 <li class="listitem"><pre class="literallayout"><span class="identifier">this_type</span> <span class="special">&amp;</span> <a name="idp770275552-bb"></a><span class="keyword">operator</span><span class="special">/=</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&amp;</span> val<span class="special">)</span><span class="special">;</span></pre></li>
 141 </ol></div>
 142 </div>
 143 <div class="refsect2">
 144 <a name="idp588623200"></a><h3>
 145 <a name="idp770317120-bb"></a><code class="computeroutput">quantity</code> public static functions</h3>
 146 <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
 147 <pre class="literallayout"><span class="keyword">static</span> <span class="identifier">this_type</span> <a name="idp770317680-bb"></a><span class="identifier">from_value</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&amp;</span> val<span class="special">)</span><span class="special">;</span></pre>Construct quantity directly from <code class="computeroutput">value_type</code>. </li></ol></div>
 148 </div>
 149 </div>
 150 </div>
 151 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 152 <td align="left"></td>
 153 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2008 Matthias Christian Schabel<br>Copyright &#169; 2007-2010 Steven
 154       Watanabe<p>
 155         Distributed under the Boost Software License, Version 1.0. (See accompanying
 156         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
 157       </p>
 158 </div></td>
 159 </tr></table>
 160 <hr>
 161 <div class="spirit-nav">
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