how to do for loop based on a limit in Ant

问题

In Ant-contrib, we can do something like:

<for list="a,b,c,d" param="instence">

But if I don't have a list, I only have a limit, e.g. limit=4.

Is there a way to do for loop based on limit, like:

<for limit="4" param="index">

回答1:

The Ant addon Flaka provides some solutions for your problem.

1) Use a while loop

the test attribute evaluates some EL expression,
which maybe a simple counter, f.e.

<project name="demo" xmlns:fl="antlib:it.haefelinger.flaka">

 <!-- some counter -->
 <fl:let>
  countdown = 3
 </fl:let>

 <fl:while test=" countdown >= 0 ">
  <fl:echo>
   #{countdown > 0 ? countdown : 'bang!' }..
  </fl:echo>
  <fl:let>
   countdown = countdown - 1
  </fl:let>
 </fl:while>

</project>

output:

  [fl:echo] 3..
  [fl:echo] 2..
  [fl:echo] 1..
  [fl:echo] bang!..

or some other expression, f.e. checking for existence of a file, means looping until some file exists :

 <fl:while test=" !'/home/rosebud/stop'.tofile.isfile ">
  <fl:echo>
   still working..
  </fl:echo>
 </fl:while>

2) Use a for loop with break or continue :

<project name="demo" xmlns:fl="antlib:it.haefelinger.flaka">

 <fl:for var="i" in=" list(1,2,3,4,5,6) ">
    <fl:echo>i = #{i}</fl:echo>
    <fl:break test=" i == 3 " />
 </fl:for>

  <fl:for var="i" in=" list(1,2,3,4,5,6) ">
    <fl:continue test=" i > 3 " />
    <fl:echo>i = #{i}</fl:echo>
 </fl:for>

</project>

which gives the same result :

  [fl:echo] i = 1
  [fl:echo] i = 2
  [fl:echo] i = 3

See more details in the Flaka manual

回答2:

<project name="Attachments" default="print">
    <property name="numAttachments" value="20" />
    <target name="generate">
        <script language="javascript"><![CDATA[
            var list = '1';
            var limit = project.getProperty( "numAttachments" );
            for (var i=2;i<limit;i++)
            { 
                list = list + ',' + i;
            }
            project.setNewProperty("list", list);            
        ]]>
        </script>    
    </target>
    <target name="print" depends="generate">
        <for list="${list}" param="letter">
            <sequential>
                <echo>Letter @{letter}</echo>
            </sequential>
        </for>
    </target>
</project>

回答3:

Its not exactly what you want, but this page has an example. Essentially, you pass in the limit as a list of numbers. Its not elegant, but it works.

Here's another idea - see the answer by user "cn1h". Its a cool way to get around limitations in ANT - embed a script from another language which can do what you want. Nice!

回答4:

In antcontrib you can also do:

<for param="index" end="@{numberOfIterations}" start="1">

But be aware of a bug: It is unable to handle begin and end being the same. So when "numberOfIterations" equals 1 you get an error.

We got a workaround for this, checking the value of numberOfIterations first and only when its not 1 doing the for-statement.

<if><equals  arg1="1" arg2="@{numberOfIterations}"/>
<then>
   ....
</then>
<else>
   <for param="index" end="@{numberOfIterations}" start="1">
   ....
</else>
</if>

来源：https://stackoverflow.com/questions/7655735/how-to-do-for-loop-based-on-a-limit-in-ant

标签

ant-contrib