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| <html lang="en"> |
| |
| <head> |
| <link rel="stylesheet" type="text/css" href="../stylesheets/style.css"> |
| <title>Local Task</title> |
| </head> |
| |
| <body> |
| |
| <h2>Local</h2> |
| <p><em>Since Ant 1.8</em></p> |
| <h3>Description</h3> |
| <p>Adds a local property to the current scope. Property scopes exist at Apache Ant's various "block" |
| levels. These include targets as well as the <a href="parallel.html">Parallel</a> |
| and <a href="sequential.html">Sequential</a> task containers |
| (including <a href="macrodef.html">Macrodef</a> bodies). A local property at a given scope "shadows" |
| properties of the same name at higher scopes, including the global scope. Note that using |
| the <code>Local</code> task at the global level effectively makes the property local to the |
| "anonymous target" in which top-level operations are carried out; it will not be defined for other |
| targets in the buildfile.</p> |
| |
| <p>A property is made local if the <code><local></code> task precedes its definition. See the |
| examples section.</p> |
| |
| <h3>Parameters</h3> |
| <table class="attr"> |
| <tr> |
| <th scope="col">Attribute</th> |
| <th scope="col">Description</th> |
| <th scope="col">Required</th> |
| </tr> |
| <tr> |
| <td>name</td> |
| <td>The property to declare in the current scope</td> |
| <td>Yes</td> |
| </tr> |
| </table> |
| |
| <h3>Examples</h3> |
| |
| <h4>Temporarily shadow a global property's value</h4> |
| |
| <pre> |
| <property name="foo" value="foo"/> |
| |
| <target name="step1"> |
| <echo>Before local: foo is ${foo}</echo> |
| <local name="foo"/> |
| <property name="foo" value="bar"/> |
| <echo>After local: foo is ${foo}</echo> |
| </target> |
| |
| <target name="step2" depends="step1"> |
| <echo>In step2: foo is ${foo}</echo> |
| </target></pre> |
| |
| <p>outputs</p> |
| |
| <pre class="output"> |
| step1: |
| [echo] Before local: foo is foo |
| [echo] After local: foo is bar |
| |
| step2: |
| [echo] In step2: foo is foo</pre> |
| |
| <p>here the <code>local</code> task shadowed the global definition of <code>foo</code> for the |
| remainder of the target <q>step1</q>.</p> |
| |
| <h4>Creating thread local properties</h4> |
| |
| <pre> |
| <property name="foo" value="foo"/> |
| |
| <parallel> |
| <echo>global 1: foo is ${foo}</echo> |
| <sequential> |
| <local name="foo"/> |
| <property name="foo" value="bar.1"/> |
| <echo>First sequential: foo is ${foo}</echo> |
| </sequential> |
| <sequential> |
| <sleep seconds="1"/> |
| <echo>global 2: foo is ${foo}</echo> |
| </sequential> |
| <sequential> |
| <local name="foo"/> |
| <property name="foo" value="bar.2"/> |
| <echo>Second sequential: foo is ${foo}</echo> |
| </sequential> |
| <echo>global 3: foo is ${foo}</echo> |
| </parallel></pre> |
| |
| <p>outputs something similar to</p> |
| |
| <pre class="output"> |
| [echo] global 3: foo is foo |
| [echo] global 1: foo is foo |
| [echo] First sequential: foo is bar.1 |
| [echo] Second sequential: foo is bar.2 |
| [echo] global 2: foo is foo</pre> |
| |
| <h4>Use inside <code>macrodef</code></h4> |
| |
| <p>This probably is where <code>local</code> can be applied in the most useful way. If you needed a |
| "temporary property" inside a <code>macrodef</code> in Ant prior to Ant 1.8.0 you had to try to come |
| up with a property name that would be unique across macro invocations.</p> |
| |
| <p>Say you wanted to write a macro that created the parent directory of a given file. A naive |
| approach would be:</p> |
| |
| <pre> |
| <macrodef name="makeparentdir"> |
| <attribute name="file"/> |
| <sequential> |
| <dirname property="parent" file="@{file}"/> |
| <mkdir dir="${parent}"/> |
| </sequential> |
| </macrodef> |
| <makeparentdir file="some-dir/some-file"/></pre> |
| |
| <p>but this would create a global property <code>parent</code> on the first invocation—and |
| since properties are not mutable, any subsequent invocation will see the same value and try to |
| create the same directory as the first invocation.</p> |
| |
| <p>The recommendation prior to Ant 1.8.0 was to use a property name based on one of the macro's |
| attributes, like</p> |
| |
| <pre> |
| <macrodef name="makeparentdir"> |
| <attribute name="file"/> |
| <sequential> |
| <dirname property="parent.@{file}" file="@{file}"/> |
| <mkdir dir="${parent.@{file}}"/> |
| </sequential> |
| </macrodef></pre> |
| |
| <p>Now invocations for different files will set different properties and the directories will get |
| created. Unfortunately this "pollutes" the global properties space. In addition, it may be hard to |
| come up with unique names in some cases.</p> |
| |
| <p>Enter <code><local></code>:</p> |
| |
| <pre> |
| <macrodef name="makeparentdir"> |
| <attribute name="file"/> |
| <sequential> |
| <local name="parent"/> |
| <dirname property="parent" file="@{file}"/> |
| <mkdir dir="${parent}"/> |
| </sequential> |
| </macrodef></pre> |
| |
| <p>Each invocation gets its own property named <code>parent</code> and there will be no global |
| property of that name at all.</p> |
| |
| </body> |
| </html> |
