c:function

<c:function
  name = identifier
  as? = type_name
  visibility? = "public" | "private" | "final" | "abstract" | "hidden" >
  <!-- Content: (c:param*, sequence-constructor) -->
</c:function>

Defines a function.

Category
declaration
Permitted parent elements
c:module
c:override
c:package

Attributes

as The return type. Omit this attribute for void functions.
name The name of the function.
visibility Specifies how the current component can be used in other (using) packages.

In addition to the attributes in the preceding table, there are a number of standard attributes that may appear on any XCST element.

Remarks

While c:template is optimized for content (markup, text), c:function is optimized for logic. Functions can be called from C# code, because it compiles to a regular method. See the table below for more differences.

feature c:template c:function
Implicit output yes no
Invocation method c:call-template C# (e.g. Foo())
Parameter binding by name by position
Tunnel parameters yes no

Because functions don’t have an implicit output, to return a value you need to use the c:return instruction, or return from code in a c:script element.

Example: Returning from a c:script Element
<c:function name='Truncate' as='string'>
   <c:param name='s' as='string'/>
   <c:param name='maxLength' as='int'/>
   <c:param name='suffix'>…</c:param>

   <c:script>
      <![CDATA[

      if (string.IsNullOrEmpty(s)) {
         return string.Empty;
      }

      if (s.Length <= maxLength) {
         return s;
      }

      return string.Concat(s.Substring(0, maxLength - suffix.Length), suffix);
      ]]>
   </c:script>
</c:function>
Example: Returning with c:return
<c:function name='MailBody' as='string'>
   <c:param name='contact' as='Contact'/>

   <c:return>
      <c:serialize method='html'>
         <a:model value='contact'>
            <dl>
               <a:display>
                  <a:member-template>
                     <dt>
                        <a:display-name/>
                        <c:text>:</c:text>
                     </dt>
                     <dd>
                        <a:display/>
                     </dd>
                  </a:member-template>
               </a:display>
            </dl>
         </a:model>
      </c:serialize>
   </c:return>
</c:function>

Function Parameters

Function parameters have several limitations, due to the fact that they compile to method parameters in C#. Type inference does not work when the value is supplied by the value attribute (defaults to Object). Default values are limited to constant expressions. The order of parameters is significant. Cannot have a parameter without a default value after one with a default value.

Note: Differences with xsl:function

As explained above, values must be returned explicitly, there’s no implicit output. c:function parameters have several limitations. c:function parameters can have default values.

Error Conditions

It is a compilation error if a c:function declaration has visibility='abstract' and the content of the element, excluding any c:param elements, is non-empty.

It is a compilation error if there’s another c:function declaration in the containing module with the same name and number of parameters.

See Also