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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 32638] Enhancement to <macrodef> to support new feature.
Date Sun, 12 Jul 2009 23:14:41 GMT
https://issues.apache.org/bugzilla/show_bug.cgi?id=32638





--- Comment #7 from SlugFiller <slugfiller@ifireball.dyndns.org>  2009-07-12 16:14:39
PST ---
The potential use of an "if" construct inside the macrodef could go beyond the
capabilities of "sequencial". Taking the "nicer" example above, supposed you
wanted the default classpath element to be no element at all, but wanted to
keep the "nicer" syntax where it is used.

You could use:
  <macrodef name="nicer">
    ...
    <element name="classpath" optional="true" useContentOnly="false" />
    <sequential>
      ...
      <java ...>
        <macroif ifTrue="classpath.element.set">
          <classpath />
        </macroif>
      </java>
    </sequential>
  </macrodef>

That way you can use:

  <nicer />
  <nicer>
    <classpath>
      <pathelement location="..." />
      <path refid="classpath" />
    </classpath>
  </nicer>

Which expands to:

  <sequential>
    ...
    <java ... />
  </sequential>
  <sequential>
    ...
    <java ...>
      <classpath>
        <pathelement location="..." />
        <path refid="classpath" />
      </classpath>
    </java>
  </sequential>

Note the slight difference between the use of a modified "sequencial", and the
use of "marcoif" - the latter effects the expanding phase and can contain any
element, not just tasks.

One aspect I am slightly worried about is name collision: If you make an
additional macro element called classpath, you cannot enter an additional
literal classpath element. The usual solution is to use different element
names, but this doesn't work, and could become a common problem, if you want to
use the useContentOnly feature.

A possible solution is to add a special element namespace which is removed
during expansion:

  <macrodef name="namespace">
    ...
    <element name="include" namespace="element" useContentOnly="false" />
    <sequential>
      ...
      <java ...>
        <element:include />
        <include name="src/**/*.java" />
      </java>
    </sequential>
  </macrodef>

Then you can use:

  <namespace>
    <include name="plugins/**/*.java" />
  </namespace>

This would expand to:

  <sequential>
    ...
    <java ...>
      <include name="src/**/*.java" />
      <include name="plugins/**/*.java" />
    </java>
  </sequential>

Note that the namespace is only used in the macrodef, not the macro instance
nor the expansion, otherwise it wouldn't add anything to just using a different
name. An alternative to a namespace would be to give an alias which is only
used inside the macrodef:

  <macrodef name="namespace">
    ...
    <element name="include" alias="moreinclude" useContentOnly="false" />
    <sequential>
      ...
      <java ...>
        <moreinclude />
        <include name="plugins/**/*.java" />
      </java>
    </sequential>
  </macrodef>

The usage and expansion are the same as above. An alternative, more
self-explanatory name for the attribute could be "internally" or
"internalName".
One could take this one step further by having different element names during
macro instance and post expansion, but that might be overkill.

Not sure how useful all of this is, but it would certainly add some nice
possibilities.

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