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From "Phil Weighill-Smith" <phil.weighill-sm...@volantis.com>
Subject RE: A possible solution for conditional execution of tasks?
Date Sun, 29 May 2005 10:22:06 GMT
My opinion regarding the disadvantages of this approach:

*	Antcall has to create a whole new Project in memory in order to work and is therefore an
inefficient task
*	If something invoked via Antcall depends on a target that is also depended on by something
depending on the target invoking Antcall then this dependency target will be executed more
than once because dependencies are not handled across Antcall invocations
*	The dependency tree is "interrupted" and graphing tools that can show ant build script structures
will not (generally) work correctly and show the whole dependency tree

It might be better to add "if" and "unless" to the standard ant Task to allow for conditional
execution, or even add a nested "condition" to the standard ant Task to allow for conditional
execution. To provide BC with the standard "execute" method, the condition/if/unless processing
would need to happen outside this method.
 
Phil :n.

	-----Original Message----- 
	From: Sandip Chitale [mailto:Sandip.Chitale@Sun.COM] 
	Sent: Sat 28/05/2005 18:56 
	To: dev@ant.apache.org 
	Cc: 
	Subject: A possible solution for conditional execution of tasks?
	
	

	To conditionally execute a step in Ant one has to resort to setting up a
	target structure like this:
	
	:
	<target name="predicate">
	   <condition property="condition-satisfied">
	       <available .../>
	   :
	   </condition>
	</target>
	
	<target name="conditional-step" if="condition-satisfied">
	   <!-- conditional tasks here -->
	   :
	   :
	</target>
	
	<target name="conditional" depends="predicate, conditional-step"/>
	
	<target name="main" depends="conditional">
	   :
	   :
	</target>
	:
	
	This is because of several reasons:
	
	    * The ant tasks do not have something like *if* attribute.
	    * One cannot get away with only two targets instead of three because
	      the dependencies are executed before the dependent. Using the
	      above example it is not possible to do what target predicate does
	      in the main target and avoid using the predicate target.
	    * Ensure order of execution
	
	However, I tried a solution making use of antcall task and it worked. It
	works as follows:
	
	:
	<target name="conditional-step" if="condition-satisfied">
	   <!-- conditional tasks here -->
	   :
	   :
	</target>
	
	<target name="main" depends="conditional-step">
	:
	   <condition property="condition-satisfied">
	       <available .../>
	   :
	   </condition>
	   <antcall target="condition-satisfied"/>
	   :
	</target>
	
	The advantage of this approach is to quickly have some tasks execute
	conditionally by putting them in a target and calling that target using
	antcall after setting some property.
	
	And it seemed to work. My question is - is there a problem using this
	approach? Why or why isn't this a preferred approach?
	
	Thanks in advance,
	Sandip
	
	

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