## PreSetDef

Since Apache Ant 1.6

### Description

The preset definition generates a new definition based on a current definition with some attributes or elements preset.

The resolution of properties in any of the attributes or nested text takes place with the definition is used and not when the preset definition is defined.

### Parameters

Attribute | Description | Required
--- | --- | ---
name | the name of the new definition | Yes
uri | The URI that this definition should live in. | No

### Parameters specified as nested elements

#### another type with attributes or elements set

The `<presetdef>` task takes one nested element as a parameter. This nested element can be any other type or task. The attributes and elements that need to be preset are placed here.

### Examples

The following fragment defines a `javac` task with the debug, deprecation, srcdir and destdir attributes set. It also has a `src` element to source files from a generated directory.

    <presetdef name="my.javac">
       <javac debug="${debug}" deprecation="${deprecation}"
              srcdir="${src.dir}" destdir="${classes.dir}">
          <src path="${gen.dir}"/>
       </javac>
    </presetdef>

This can be used as a normal `javac` task—for example:

    <my.javac/>

The attributes specified in the preset task may be overridden—i.e. they may be seen as optional attributes—for example:

    <my.javac srcdir="${test.src}" deprecation="no"/>

One may put a `presetdef` definition in an antlib. For example suppose the jar file `antgoodies.jar` has the `antlib.xml` as follows:

    <antlib>
       <taskdef resource="com/acme/antgoodies/tasks.properties"/>
       <!-- Implement the common use of the javac command -->
       <presetdef name="javac">
          <javac deprecation="${deprecation}" debug="${debug}"
                 srcdir="src" destdir="classes"/>
       </presetdef>
    </antlib>

One may then use this in a build file as follows:

    <project default="example" xmlns:antgoodies="antlib:com.acme.antgoodies">
       <target name="example">
          <!-- Compile source -->
          <antgoodies:javac srcdir="src/main"/>
          <!-- Compile test code -->
          <antgoodies:javac srcdir="src/test"/>
       </target>
    </project>

The following is an example of evaluation of properties when the definition is used:

    <target name="defineandcall">
       <presetdef name="showmessage">
          <echo>message is '${message}'</echo>
       </presetdef>
       <showmessage/>
       <property name="message" value="Message 1"/>
       <showmessage/>
       <antcall target="called">
          <param name="message" value="Message 2"/>
       </antcall>
    </target>
    <target name="called">
       <showmessage/>
    </target>

The command `ant defineandcall` results in the output:

    defineandcall:
    [showmessage] message is '${message}'
    [showmessage] message is 'Message 1'

    called:
    [showmessage] message is 'Message 2'

It is possible to use a trick to evaluate properties when the definition is made rather than used. This can be useful if you do not expect some properties to be available in child builds run with `<ant ... inheritall="false">`:

    <macrodef name="showmessage-presetdef">
      <attribute name="messageval"/>
      <presetdef name="showmessage">
        <echo>message is '@{messageval}'</echo>
      </presetdef>
    </macrodef>
    <showmessage-presetdef messageval="${message}"/>