smarty/docs/en/designers/language-custom-functions/language-function-eval.xml

<?xml version="1.0" encoding="iso-8859-1"?>
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<sect1 id="language.function.eval">
 <title>{eval}</title>
  <para>
   {eval} is used to evaluate a variable as a template. This can be used
   for things like embedding template tags/variables into variables or
   tags/variables into config file variables.
  </para>
  <para>
   If you supply the special "assign" attribute, the output of the
   {eval} function will be assigned to this template variable instead of
   being output to the template.
 </para>
 
 <informaltable frame="all">
  <tgroup cols="5">
   <colspec colname="param" align="center" />
   <colspec colname="type" align="center" />
   <colspec colname="required" align="center" />
   <colspec colname="default" align="center" />
   <colspec colname="desc" />
   <thead>
    <row>
     <entry>Attribute Name</entry>
     <entry>Type</entry>
     <entry>Required</entry>
     <entry>Default</entry>
     <entry>Description</entry>
    </row>
   </thead>
   <tbody>
    <row>
     <entry>var</entry>
     <entry>mixed</entry>
     <entry>Yes</entry>
     <entry><emphasis>n/a</emphasis></entry>
     <entry>variable (or string) to evaluate</entry>
    </row>
    <row>
     <entry>assign</entry>
     <entry>string</entry>
     <entry>No</entry>
     <entry><emphasis>n/a</emphasis></entry>
     <entry>the template variable the output will be assigned
      to</entry>
    </row>
   </tbody>
  </tgroup>
 </informaltable>

 <note>
  <title>Technical Note</title>
  <para>
   Evaluated variables are treated the same as templates. They follow
   the same escapement and security features just as if they were
   templates.
  </para>
 </note>
 <note>
  <title>Technical Note</title>
  <para>
   Evaluated variables are compiled on every invocation, the compiled
   versions are not saved! However if you have
   <link linkend="caching">caching</link>
   enabled, the
   output will be cached with the rest of the template.
  </para>
 </note>
 <example>
  <title>{eval}</title>
  <programlisting>
<![CDATA[
   setup.conf
   ----------

   emphstart = <strong>
   emphend = </strong>
   title = Welcome to {$company}'s home page!
   ErrorCity = You must supply a {#emphstart#}city{#emphend#}.
   ErrorState = You must supply a {#emphstart#}state{#emphend#}.
]]>
  </programlisting>
  <para>
   Where index.tpl is:
  </para>
  <programlisting>
<![CDATA[
   {config_load file="setup.conf"}

   {eval var=$foo}
   {eval var=#title#}
   {eval var=#ErrorCity#}
   {eval var=#ErrorState# assign="state_error"}
   {$state_error}
]]>
  </programlisting>
  <para>
   The above example will output:
  </para>
  <screen>
<![CDATA[
   This is the contents of foo.
   Welcome to Foobar Pub & Grill's home page!
   You must supply a <strong>city</strong>.
   You must supply a <strong>state</strong>.

]]>
  </screen>
 </example>
</sect1>
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