Re: Simulating null parameters in macros

You can check if it's not a scalar first:

<#if !param1?is_scalar || param1 != null)>

On Jul 5, 2011, at 9:21 AM, Hinkle, Cameron wrote:

> 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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All of the data generated in your IT infrastructure is seriously valuable.
Why? It contains a definitive record of application performance, security 
threats, fraudulent activity, and more. Splunk takes this data and makes 
sense of it. IT sense. And common sense.
http://p.sf.net/sfu/splunk-d2d-c2

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