Is it possible to assign default values to NAnt properties? - nant

Question

I'd like to use the property value as a part of an argument passed to a certain EXE via <exec/> task. There's a condition which influences the property initialization, that is, if condition is true, it should contain value, otherwise be just empty (but still defined).
This is what I ended up so far:
<property name="prop1" value="" />
<property name="prop1" value="some-value-based-on-condition" if="condition-goes-here" />
And later on:
<exec program="my.exe">
<arg value="C:\Root\Folder\${prop1}" />
...
</exec>
If the property is not set, I'd like to pass just C:\Root\Folder\ as an argument value.
Initializing the property in this way seems too much for such a simple operation. Is there a way to do it simpler using what's in NAnt at the moment? I would imagine something like:
<property name="prop1" value="somevalue-based-on-condition" if="condition" default="" />

Answer 1

The example below should meet your needs. It will create a property named 'SolutionConfiguration' and assign it the value 'Release' if and only if the same parameter isn't already defined (ie. it was defined via the command line).
<property name="SolutionConfiguration" value="Release" unless="${property::exists('SolutionConfiguration')}" />
For your scenario, try
<property name="RootFolder" value="c:\Root\Folder" unless="${property::exists('RootFolder')}" />
<exec program="my.exe">
<arg value="${RootFolder}\${prop1}" />
...
</exec>

Answer 2

Use overwrite="False"
<property name="RootFolder" value="c:\Root\Folder" overwrite="false" />