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| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="spirit.qi.tutorials.employee___parsing_into_structs"></a><a class="link" href="employee___parsing_into_structs.html" title="Employee - Parsing into structs">Employee |
| - Parsing into structs</a> |
| </h4></div></div></div> |
| <p> |
| It's a common question in the <a href="http://www.nabble.com/The-Spirit-Parser-Library-f3430.html" target="_top">Spirit |
| General List</a>: How do I parse and place the results into a C++ struct? |
| Of course, at this point, you already know various ways to do it, using |
| semantic actions. There are many ways to skin a cat. Spirit2, being fully |
| attributed, makes it even easier. The next example demonstrates some features |
| of Spirit2 that make this easy. In the process, you'll learn about: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| More about attributes |
| </li> |
| <li class="listitem"> |
| Auto rules |
| </li> |
| <li class="listitem"> |
| Some more built-in parsers |
| </li> |
| <li class="listitem"> |
| Directives |
| </li> |
| </ul></div> |
| <p> |
| First, let's create a struct representing an employee: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">employee</span> |
| <span class="special">{</span> |
| <span class="keyword">int</span> <span class="identifier">age</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">surname</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">forename</span><span class="special">;</span> |
| <span class="keyword">double</span> <span class="identifier">salary</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Then, we need to tell <a href="../../../../../../../libs/fusion/doc/html/index.html" target="_top">Boost.Fusion</a> |
| about our employee struct to make it a first-class fusion citizen that |
| the grammar can utilize. If you don't know fusion yet, it is a <a href="http://www.boost.org/" target="_top">Boost</a> |
| library for working with heterogeneous collections of data, commonly referred |
| to as tuples. Spirit uses fusion extensively as part of its infrastructure. |
| </p> |
| <p> |
| In fusion's view, a struct is just a form of a tuple. You can adapt any |
| struct to be a fully conforming fusion tuple: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">BOOST_FUSION_ADAPT_STRUCT</span><span class="special">(</span> |
| <span class="identifier">client</span><span class="special">::</span><span class="identifier">employee</span><span class="special">,</span> |
| <span class="special">(</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">age</span><span class="special">)</span> |
| <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">surname</span><span class="special">)</span> |
| <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">forename</span><span class="special">)</span> |
| <span class="special">(</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">salary</span><span class="special">)</span> |
| <span class="special">)</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Now we'll write a parser for our employee. Inputs will be of the form: |
| </p> |
| <pre class="programlisting"><span class="identifier">employee</span><span class="special">{</span> <span class="identifier">age</span><span class="special">,</span> <span class="string">"surname"</span><span class="special">,</span> <span class="string">"forename"</span><span class="special">,</span> <span class="identifier">salary</span> <span class="special">}</span> |
| </pre> |
| <p> |
| Here goes: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">employee_parser</span> <span class="special">:</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">grammar</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">employee</span><span class="special">(),</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> |
| <span class="special">{</span> |
| <span class="identifier">employee_parser</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">employee_parser</span><span class="special">::</span><span class="identifier">base_type</span><span class="special">(</span><span class="identifier">start</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">using</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">int_</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">lit</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">double_</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">lexeme</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">char_</span><span class="special">;</span> |
| |
| <span class="identifier">quoted_string</span> <span class="special">%=</span> <span class="identifier">lexeme</span><span class="special">[</span><span class="char">'"'</span> <span class="special">>></span> <span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span> <span class="special">>></span> <span class="char">'"'</span><span class="special">];</span> |
| |
| <span class="identifier">start</span> <span class="special">%=</span> |
| <span class="identifier">lit</span><span class="special">(</span><span class="string">"employee"</span><span class="special">)</span> |
| <span class="special">>></span> <span class="char">'{'</span> |
| <span class="special">>></span> <span class="identifier">int_</span> <span class="special">>></span> <span class="char">','</span> |
| <span class="special">>></span> <span class="identifier">quoted_string</span> <span class="special">>></span> <span class="char">','</span> |
| <span class="special">>></span> <span class="identifier">quoted_string</span> <span class="special">>></span> <span class="char">','</span> |
| <span class="special">>></span> <span class="identifier">double_</span> |
| <span class="special">>></span> <span class="char">'}'</span> |
| <span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="identifier">qi</span><span class="special">::</span><span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">(),</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> <span class="identifier">quoted_string</span><span class="special">;</span> |
| <span class="identifier">qi</span><span class="special">::</span><span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">employee</span><span class="special">(),</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">></span> <span class="identifier">start</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| The full cpp file for this example can be found here: <a href="../../../../../example/qi/employee.cpp" target="_top">../../example/qi/employee.cpp</a> |
| </p> |
| <p> |
| Let's walk through this one step at a time (not necessarily from top to |
| bottom). |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">employee_parser</span> <span class="special">:</span> <span class="identifier">grammar</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">employee</span><span class="special">(),</span> <span class="identifier">space_type</span><span class="special">></span> |
| </pre> |
| <p> |
| <code class="computeroutput"><span class="identifier">employee_parser</span></code> is a grammar. |
| Like before, we make it a template so that we can reuse it for different |
| iterator types. The grammar's signature is: |
| </p> |
| <pre class="programlisting"><span class="identifier">employee</span><span class="special">()</span> |
| </pre> |
| <p> |
| meaning, the parser generates employee structs. <code class="computeroutput"><span class="identifier">employee_parser</span></code> |
| skips white spaces using <code class="computeroutput"><span class="identifier">space_type</span></code> |
| as its skip parser. |
| </p> |
| <pre class="programlisting"><span class="identifier">employee_parser</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">employee_parser</span><span class="special">::</span><span class="identifier">base_type</span><span class="special">(</span><span class="identifier">start</span><span class="special">)</span> |
| </pre> |
| <p> |
| Initializes the base class. |
| </p> |
| <pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">(),</span> <span class="identifier">space_type</span><span class="special">></span> <span class="identifier">quoted_string</span><span class="special">;</span> |
| <span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">employee</span><span class="special">(),</span> <span class="identifier">space_type</span><span class="special">></span> <span class="identifier">start</span><span class="special">;</span> |
| </pre> |
| <p> |
| Declares two rules: <code class="computeroutput"><span class="identifier">quoted_string</span></code> |
| and <code class="computeroutput"><span class="identifier">start</span></code>. <code class="computeroutput"><span class="identifier">start</span></code> has the same template parameters |
| as the grammar itself. <code class="computeroutput"><span class="identifier">quoted_string</span></code> |
| has a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code> attribute. |
| </p> |
| <a name="spirit.qi.tutorials.employee___parsing_into_structs.lexeme"></a><h6> |
| <a name="id810693"></a> |
| <a class="link" href="employee___parsing_into_structs.html#spirit.qi.tutorials.employee___parsing_into_structs.lexeme">Lexeme</a> |
| </h6> |
| <pre class="programlisting"><span class="identifier">lexeme</span><span class="special">[</span><span class="char">'"'</span> <span class="special">>></span> <span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span> <span class="special">>></span> <span class="char">'"'</span><span class="special">];</span> |
| </pre> |
| <p> |
| <code class="computeroutput"><span class="identifier">lexeme</span></code> inhibits space skipping |
| from the open brace to the closing brace. The expression parses quoted |
| strings. |
| </p> |
| <pre class="programlisting"><span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span> |
| </pre> |
| <p> |
| parses one or more chars, except the double quote. It stops when it sees |
| a double quote. |
| </p> |
| <a name="spirit.qi.tutorials.employee___parsing_into_structs.difference"></a><h6> |
| <a name="id810806"></a> |
| <a class="link" href="employee___parsing_into_structs.html#spirit.qi.tutorials.employee___parsing_into_structs.difference">Difference</a> |
| </h6> |
| <p> |
| The expression: |
| </p> |
| <pre class="programlisting"><span class="identifier">a</span> <span class="special">-</span> <span class="identifier">b</span> |
| </pre> |
| <p> |
| parses <code class="computeroutput"><span class="identifier">a</span></code> but not <code class="computeroutput"><span class="identifier">b</span></code>. Its attribute is just <code class="computeroutput"><span class="identifier">A</span></code>; the attribute of <code class="computeroutput"><span class="identifier">a</span></code>. |
| <code class="computeroutput"><span class="identifier">b</span></code>'s attribute is ignored. |
| Hence, the attribute of: |
| </p> |
| <pre class="programlisting"><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span> |
| </pre> |
| <p> |
| is just <code class="computeroutput"><span class="keyword">char</span></code>. |
| </p> |
| <a name="spirit.qi.tutorials.employee___parsing_into_structs.plus"></a><h6> |
| <a name="id810914"></a> |
| <a class="link" href="employee___parsing_into_structs.html#spirit.qi.tutorials.employee___parsing_into_structs.plus">Plus</a> |
| </h6> |
| <pre class="programlisting"><span class="special">+</span><span class="identifier">a</span> |
| </pre> |
| <p> |
| is similar to Kleene star. Rather than match everything, <code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code> matches |
| one or more. Like it's related function, the Kleene star, its attribute |
| is a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span></code> |
| where <code class="computeroutput"><span class="identifier">A</span></code> is the attribute |
| of <code class="computeroutput"><span class="identifier">a</span></code>. So, putting all these |
| together, the attribute of |
| </p> |
| <pre class="programlisting"><span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span> |
| </pre> |
| <p> |
| is then: |
| </p> |
| <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> |
| </pre> |
| <a name="spirit.qi.tutorials.employee___parsing_into_structs.sequence_attribute"></a><h6> |
| <a name="id811050"></a> |
| <a class="link" href="employee___parsing_into_structs.html#spirit.qi.tutorials.employee___parsing_into_structs.sequence_attribute">Sequence |
| Attribute</a> |
| </h6> |
| <p> |
| Now what's the attribute of |
| </p> |
| <pre class="programlisting"><span class="char">'"'</span> <span class="special">>></span> <span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span> <span class="special">>></span> <span class="char">'"'</span> |
| </pre> |
| <p> |
| ? |
| </p> |
| <p> |
| Well, typically, the attribute of: |
| </p> |
| <pre class="programlisting"><span class="identifier">a</span> <span class="special">>></span> <span class="identifier">b</span> <span class="special">>></span> <span class="identifier">c</span> |
| </pre> |
| <p> |
| is: |
| </p> |
| <pre class="programlisting"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">,</span> <span class="identifier">C</span><span class="special">></span> |
| </pre> |
| <p> |
| where <code class="computeroutput"><span class="identifier">A</span></code> is the attribute |
| of <code class="computeroutput"><span class="identifier">a</span></code>, <code class="computeroutput"><span class="identifier">B</span></code> |
| is the attribute of <code class="computeroutput"><span class="identifier">b</span></code> and |
| <code class="computeroutput"><span class="identifier">C</span></code> is the attribute of |
| <code class="computeroutput"><span class="identifier">c</span></code>. What is <code class="computeroutput"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span></code>? - a tuple. |
| </p> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| If you don't know what I am talking about, see: <a href="http://tinyurl.com/6xun4j" target="_top">Fusion |
| Vector</a>. It might be a good idea to have a look into <a href="../../../../../../../libs/fusion/doc/html/index.html" target="_top">Boost.Fusion</a> |
| at this point. You'll definitely see more of it in the coming pages. |
| </p></td></tr> |
| </table></div> |
| <a name="spirit.qi.tutorials.employee___parsing_into_structs.attribute_collapsing"></a><h6> |
| <a name="id811272"></a> |
| <a class="link" href="employee___parsing_into_structs.html#spirit.qi.tutorials.employee___parsing_into_structs.attribute_collapsing">Attribute |
| Collapsing</a> |
| </h6> |
| <p> |
| Some parsers, especially those very little literal parsers you see, like |
| <code class="computeroutput"><span class="char">'"'</span></code>, do not have attributes. |
| </p> |
| <p> |
| Nodes without attributes are disregarded. In a sequence, like above, all |
| nodes with no attributes are filtered out of the <code class="computeroutput"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span></code>. |
| So, since <code class="computeroutput"><span class="char">'"'</span></code> has no attribute, |
| and <code class="computeroutput"><span class="special">+(</span><span class="identifier">char_</span> |
| <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span></code> has a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span></code> attribute, the whole expression's attribute |
| should have been: |
| </p> |
| <pre class="programlisting"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> <span class="special">></span> |
| </pre> |
| <p> |
| But wait, there's one more collapsing rule: If the attribute is followed |
| by a single element <code class="computeroutput"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span></code>, |
| The element is stripped naked from its container. To make a long story |
| short, the attribute of the expression: |
| </p> |
| <pre class="programlisting"><span class="char">'"'</span> <span class="special">>></span> <span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span> <span class="special">>></span> <span class="char">'"'</span> |
| </pre> |
| <p> |
| is: |
| </p> |
| <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> |
| </pre> |
| <a name="spirit.qi.tutorials.employee___parsing_into_structs.auto_rules"></a><h6> |
| <a name="id811511"></a> |
| <a class="link" href="employee___parsing_into_structs.html#spirit.qi.tutorials.employee___parsing_into_structs.auto_rules">Auto |
| Rules</a> |
| </h6> |
| <p> |
| It is typical to see rules like: |
| </p> |
| <pre class="programlisting"><span class="identifier">r</span> <span class="special">=</span> <span class="identifier">p</span><span class="special">[</span><span class="identifier">_val</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">];</span> |
| </pre> |
| <p> |
| If you have a rule definition such as the above, where the attribute of |
| the RHS (right hand side) of the rule is compatible with the attribute |
| of the LHS (left hand side), then you can rewrite it as: |
| </p> |
| <pre class="programlisting"><span class="identifier">r</span> <span class="special">%=</span> <span class="identifier">p</span><span class="special">;</span> |
| </pre> |
| <p> |
| The attribute of <code class="computeroutput"><span class="identifier">p</span></code> automatically |
| uses the attribute of <code class="computeroutput"><span class="identifier">r</span></code>. |
| </p> |
| <p> |
| So, going back to our <code class="computeroutput"><span class="identifier">quoted_string</span></code> |
| rule: |
| </p> |
| <pre class="programlisting"><span class="identifier">quoted_string</span> <span class="special">%=</span> <span class="identifier">lexeme</span><span class="special">[</span><span class="char">'"'</span> <span class="special">>></span> <span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span> <span class="special">>></span> <span class="char">'"'</span><span class="special">];</span> |
| </pre> |
| <p> |
| is a simplified version of: |
| </p> |
| <pre class="programlisting"><span class="identifier">quoted_string</span> <span class="special">=</span> <span class="identifier">lexeme</span><span class="special">[</span><span class="char">'"'</span> <span class="special">>></span> <span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span> <span class="special">>></span> <span class="char">'"'</span><span class="special">][</span><span class="identifier">_val</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">];</span> |
| </pre> |
| <p> |
| The attribute of the <code class="computeroutput"><span class="identifier">quoted_string</span></code> |
| rule: <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code> <span class="bold"><strong>is compatible</strong></span> |
| with the attribute of the RHS: <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span></code>. The RHS extracts the parsed attribute |
| directly into the rule's attribute, in-situ. |
| </p> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| <code class="computeroutput"><span class="identifier">r</span> <span class="special">%=</span> |
| <span class="identifier">p</span></code> and <code class="computeroutput"><span class="identifier">r</span> |
| <span class="special">=</span> <span class="identifier">p</span></code> |
| are equivalent if there are no semantic actions associated with <code class="computeroutput"><span class="identifier">p</span></code>. |
| </p></td></tr> |
| </table></div> |
| <a name="spirit.qi.tutorials.employee___parsing_into_structs.finally"></a><h6> |
| <a name="id813039"></a> |
| <a class="link" href="employee___parsing_into_structs.html#spirit.qi.tutorials.employee___parsing_into_structs.finally">Finally</a> |
| </h6> |
| <p> |
| We're down to one rule, the start rule: |
| </p> |
| <pre class="programlisting"><span class="identifier">start</span> <span class="special">%=</span> |
| <span class="identifier">lit</span><span class="special">(</span><span class="string">"employee"</span><span class="special">)</span> |
| <span class="special">>></span> <span class="char">'{'</span> |
| <span class="special">>></span> <span class="identifier">int_</span> <span class="special">>></span> <span class="char">','</span> |
| <span class="special">>></span> <span class="identifier">quoted_string</span> <span class="special">>></span> <span class="char">','</span> |
| <span class="special">>></span> <span class="identifier">quoted_string</span> <span class="special">>></span> <span class="char">','</span> |
| <span class="special">>></span> <span class="identifier">double_</span> |
| <span class="special">>></span> <span class="char">'}'</span> |
| <span class="special">;</span> |
| </pre> |
| <p> |
| Applying our collapsing rules above, the RHS has an attribute of: |
| </p> |
| <pre class="programlisting"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="keyword">double</span><span class="special">></span> |
| </pre> |
| <p> |
| These nodes do not have an attribute: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| <code class="computeroutput"><span class="identifier">lit</span><span class="special">(</span><span class="string">"employee"</span><span class="special">)</span></code> |
| </li> |
| <li class="listitem"> |
| <code class="computeroutput"><span class="char">'{'</span></code> |
| </li> |
| <li class="listitem"> |
| <code class="computeroutput"><span class="char">','</span></code> |
| </li> |
| <li class="listitem"> |
| <code class="computeroutput"><span class="char">'}'</span></code> |
| </li> |
| </ul></div> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| In case you are wondering, <code class="computeroutput"><span class="identifier">lit</span><span class="special">(</span><span class="string">"employee"</span><span class="special">)</span></code> is the same as "employee". |
| We had to wrap it inside <code class="computeroutput"><span class="identifier">lit</span></code> |
| because immediately after it is <code class="computeroutput"><span class="special">>></span> |
| <span class="char">'{'</span></code>. You can't right-shift a <code class="computeroutput"><span class="keyword">char</span><span class="special">[]</span></code> |
| and a <code class="computeroutput"><span class="keyword">char</span></code> - you know, C++ |
| syntax rules. |
| </p></td></tr> |
| </table></div> |
| <p> |
| Recall that the attribute of <code class="computeroutput"><span class="identifier">start</span></code> |
| is the <code class="computeroutput"><span class="identifier">employee</span></code> struct: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">employee</span> |
| <span class="special">{</span> |
| <span class="keyword">int</span> <span class="identifier">age</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">surname</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">forename</span><span class="special">;</span> |
| <span class="keyword">double</span> <span class="identifier">salary</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Now everything is clear, right? The <code class="computeroutput"><span class="keyword">struct</span> |
| <span class="identifier">employee</span></code> <span class="bold"><strong>IS</strong></span> |
| compatible with <code class="computeroutput"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="keyword">double</span><span class="special">></span></code>. So, the RHS of <code class="computeroutput"><span class="identifier">start</span></code> |
| uses start's attribute (a <code class="computeroutput"><span class="keyword">struct</span> |
| <span class="identifier">employee</span></code>) in-situ when it does |
| its work. |
| </p> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2001-2010 Joel de Guzman, Hartmut Kaiser<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| 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>) |
| </p> |
| </div></td> |
| </tr></table> |
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