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From "Steve Cohen" <Ste...@ignitesports.com>
Subject [PROPOSE] task parameters that are only supplied when a property is defined
Date Fri, 08 Mar 2002 16:53:06 GMT
I previously sent this idea in a message whose title may have hidden its importance, but this
is an idea I'd really like to see and I'd like the developers to comment on it.

What if there were a convenient syntax within ant for specifying task attributes based on
properties 

such that

if the property were not set 
	the task code would never see the attribute?

In other words, for example, look at this call:
  <stcheckout URL="STARTEAM:49201/Aproject/AView"
     username="auser"
     password="secret"
     rootlocalfolder="C:\dev\buildtest\co"
     forced="true" 
     label = "${lbl}"  
  />

If the lbl property is defined, the task will get its value as the label attribute.  But if
the lbl property is not defined, the task will get the text "${lbl}" and most likely fail.

I am proposing a new syntax that would allow a property to be specified with a different meaning.
 Let's say this syntax is two dollar signs instead of one ($${property}).  (This may not be
the optimal symbol for the ant parser, but that is a detail - I am not wedded to any symbol).

Using this syntax, the above example becomes:

  <stcheckout URL="STARTEAM:49201/Aproject/AView"
     username="auser"
     password="secret"
     rootlocalfolder="C:\dev\buildtest\co"
     forced="true" 
     label = "$${lbl}"  
  />

My proposal is that this syntax be interpreted this way:

If the property lbl is defined, treat $${lbl} exactly as ${lbl} but
if the property lbl is not defined, do not even pass the label attribute to the task.

It seems to me that this would allow for much more flexible scripts, especially when more
than one parameter of a task is optional and there are different use cases for the task. 
In the above example, to get the variable functionality desired, I must include two blocks
in my script, one with the label attribute defined and the other without it, and put it some
conditionals to direct the processing to the right place.  This can get clumsy, especially
if there are several attributes to parameterize; the combinatorial possiblilities could be
large, making for scripts that are harder to understand or maintain.





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