Simulating null parameters in macros

I asked this question on Stack Overflow but no one seemed to have an answer for me.  Hoping someone here will:

http://stackoverflow.com/questions/6553004/simulate-null-parameters-in-freemarker-macros



I'm building a site using Freemarker and have started heavily using macros. I know in Freemarker 2.3 that passing a null value into a macro as a parameter is equivalent to not passing a parameter at all so I've created a global variable called "null" to simulate null checking in my macros:

<#assign null="NUL" />

Now in my macros I can do this:

<#maco doSomething param1=null>

  <#if param1 != null>

    <div>WIN!</div>

  </#if>

</#macro>

The problem comes if I want to pass a parameter that isn't a scalar. For instance, passing a List (which in Freemarker is a SimpleSequence) to a macro and checking against my null keyword yields the error:

freemarker.template.TemplateException: The only legal comparisons are between two numbers, two strings, or two dates. Left hand operand is a freemarker.template.SimpleSequence Right hand operand is a freemarker.template.SimpleScalar

I took a look at the freemarker code and I can see the issue (ComparisonExpression.isTrue()):

if(ltm instanceof TemplateNumberModel && rtm instanceof TemplateNumberModel) {

  ...

}

else if(ltm instanceof TemplateDateModel && rtm instanceof TemplateDateModel) {

  ...

}

else if(ltm instanceof TemplateScalarModel && rtm instanceof TemplateScalarModel) {

  ...

}

else if(ltm instanceof TemplateBooleanModel && rtm instanceof TemplateBooleanModel) {

  ...

}

// Here we handle compatibility issues

else if(env.isClassicCompatible()) {

  ...

}

else {

  throw new TemplateException("The only legal comparisons...", env);

}

So the only solution I can think of is to set isClassicCompatible to true, which I think will call toString() on both objects and compare the result. However, the documentation specifically says anything relying on old features should be rewritten.

My quesion is, is there a solution to this that doesn't rely on deprecated features?


Thanks,
Cameron

Cameron Hinkle  |  Senior Application Engineer  |  Nike DCIT  |  503.532.3075  |  7. Evolve Immediately |

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