Local

Description

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 Parallel and Sequential task containers (including Macrodef 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 Local 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. Since Ant 1.8

A property is made local if the <local> task precedes its definition. See the examples section.

Parameters

Examples

Temporarily shadow a global property's value

    <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>

outputs

step1:
     [echo] Before local: foo is foo
     [echo] After local: foo is bar

step2:
     [echo] In step2: foo is foo

here the local-task shadowed the global definition of foo for the remainder of the target step1.

Creating thread local properties

    <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>

outputs something similar to

     [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

Use inside macrodef

This probably is where local can be applied in the most useful way. If you needed a "temporary property" inside a macrodef 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.

Say you wanted to write a macro that created the parent directory of a given file. A naive approach would be:

    <macrodef name="makeparentdir">
        <attribute name="file"/>
        <sequential>
            <dirname property="parent" file="@{file}"/>
            <mkdir dir="${parent}"/>
        </sequential>
    </macrodef>
    <makeparentdir file="some-dir/some-file"/>

but this would create a global property "parent" 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.

The recommendation prior to Ant 1.8.0 was to use a property name based on one of the macro's attributes, like

    <macrodef name="makeparentdir">
        <attribute name="file"/>
        <sequential>
            <dirname property="parent.@{file}" file="@{file}"/>
            <mkdir dir="${parent.@{file}}"/>
        </sequential>
    </macrodef>

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.

Enter <local>:

    <macrodef name="makeparentdir">
        <attribute name="file"/>
        <sequential>
            <local name="parent"/>
            <dirname property="parent" file="@{file}"/>
            <mkdir dir="${parent}"/>
        </sequential>
    </macrodef>

Each invocation gets its own property name "parent" and there will be no global property of that name at all.