| <?xml version="1.0" standalone="no"?> |
| <!DOCTYPE s1 SYSTEM "../../style/dtd/document.dtd"> |
| <!-- |
| * The Apache Software License, Version 1.1 |
| * |
| * |
| * Copyright (c) 2001 The Apache Software Foundation. All rights |
| * reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * |
| * 1. Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * |
| * 2. Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in |
| * the documentation and/or other materials provided with the |
| * distribution. |
| * |
| * 3. The end-user documentation included with the redistribution, |
| * if any, must include the following acknowledgment: |
| * "This product includes software developed by the |
| * Apache Software Foundation (http://www.apache.org/)." |
| * Alternately, this acknowledgment may appear in the software itself, |
| * if and wherever such third-party acknowledgments normally appear. |
| * |
| * 4. The names "Xalan" and "Apache Software Foundation" must |
| * not be used to endorse or promote products derived from this |
| * software without prior written permission. For written |
| * permission, please contact apache@apache.org. |
| * |
| * 5. Products derived from this software may not be called "Apache", |
| * nor may "Apache" appear in their name, without prior written |
| * permission of the Apache Software Foundation. |
| * |
| * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED |
| * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
| * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE |
| * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR |
| * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF |
| * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND |
| * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, |
| * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT |
| * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
| * SUCH DAMAGE. |
| * ==================================================================== |
| * |
| * This software consists of voluntary contributions made by many |
| * individuals on behalf of the Apache Software Foundation and was |
| * originally based on software copyright (c) 2001, Sun |
| * Microsystems., http://www.sun.com. For more |
| * information on the Apache Software Foundation, please see |
| * <http://www.apache.org/>. |
| --> |
| <s1 title="<xsl:choose> / <xsl:when> / <xsl:otherwise>"> |
| |
| <s2 title="Contents"> |
| <ul> |
| <li><link anchor="functionality">Functionality</link></li> |
| <li><link anchor="implementation">Implementation</link></li> |
| </ul> |
| </s2> |
| |
| <anchor name="functionality"/> |
| <s2 title="Functionality"> |
| |
| <p>The <code><xsl:choose></code> element is used to determine one |
| course of action based on a series of tests. Each test is done inside an |
| <code><xsl:when></code> element. If a test succeeds, the body of the |
| <code><xsl:when></code> element is executed. If no tests fail then |
| a <code><xsl:otherwise></code> element can be used to specify a |
| default action:</p> |
| |
| <source> |
| <xsl:choose> |
| <xsl:when test="element-available('some-extension')"> |
| ... |
| </xsl:when> |
| <xsl:when test="function-availabe('saxon:nodeset')"> |
| ... |
| </xsl:when> |
| <xsl:otherwise> |
| ... |
| </xsl:otherwise> |
| </xsl:choose></source> |
| |
| </s2> |
| |
| <anchor name="implementation"/> |
| <s2 title="Implementation"> |
| |
| <p>The <code>Choose</code> class places all <code>When</code> child-nodes |
| in a vector. The <code>Choose</code> class translates the "test"-attribute |
| of all <code>When</code> nodes (in strict order) and chains them together |
| in an if-else style. The expression that holds each test contains a true- |
| and a false-list. These lists are vectors of branch targets that should be |
| used if the test succeeds or fails, respectively. The first test's |
| false-list is pointed to the start of the next test (ie. if the first test |
| fails, then we run the next test). The last test's false-list points directly |
| to the code for the body of the <code><xsl:otherwise></code> element. |
| </p> |
| |
| <p>Just as with the <code><xsl:if></code>-element, special care is |
| taken for the <code>element-available()</code> and |
| <code>function-available()</code> functions. These functions are evaluated at |
| compile-time (this can be done since all parameters for these functions are |
| literals) and the body of a <code><xsl:when></code> element is not |
| compiled if we know that it will never be needed at runtime.</p> |
| |
| </s2> |
| |
| </s1> |