Working with simple ant's property is tricky & doesn't allow to set needed value easily (properties are immutable). Using ant-conrib's var tasks allows properties to be set and unset.
Any genuinue or good reason behind making ant property designed to work in such a complex way?.
<property name="some.ant.prop" value=""/>
<if>
<isset property="some.ant.prop"/>
<then>
<echo message="immutable ant prop - not good, defined and just even set to null string : ${some.ant.prop}"/>
<property name="some.ant.prop" value="no-effect-value"/>
<echo message="no-effect on changing already defined prop : ${some.ant.prop}"/>
<var name="some.ant.prop" unset="true"/>
<property name="some.ant.prop" value="any-value-accepted"/>
<echo message="Overwritten prop value: ${some.ant.prop}"/>
</then>
</if>
Not for discussion or argument , but its good to know on more feasible alternatives. Thanks.
Ant ain't a programming language !
Properties once set are immutable in ant by design.
The Pros and Cons have been discussed (much too) often and i won't go into details.
Several possibilities to get over those limitations :
In the past people used antcall for that purpose - with all its drawbacks, search for 'antcall vs. macrodef' to get the details. Ant 1.6 introduced macrodef and Ant 1.8 came with a new local task.
If macrodef and local are not sufficient you may use script task with builtin javascript engine (since JDK 1.6) or Groovy to access ant api.
There are also Ant addons like f.e. antcontrib or Flaka. If antcontrib var / unset feels too clumsy for you, the
Flaka's let task provides a more straight approach for overwriting properties :
<!-- set a new property -->
<fl:let>foo := 'bar'</fl:let>
<!-- overwrite an existing property or userproperty
(those properties defined on the commandline via -Dfoo=bar ..)
notice the double '::' in foo ::= 'baz' -->
<fl:let>foo ::= 'baz'</fl:let>
Finally :
Either get used to ant and its limitations (but don't use antcall !) or
use Ant addon
use ant from groovy
or switch to Gradle.