Re: Simulating null parameters in macros

Well, I have added tip for a minor improvement there... but really,
this whole null-mess will not be fixed without adding null support in
FreeMarker itself... which AFAIR can't be done without breaking BC.
/-:

-- 
Best regards,
 Daniel Dekany


Tuesday, July 5, 2011, 6:21:42 PM, 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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