Stringtemplate compare strings does not work

Question

Can someone explain why this does not work ?

StringTemplate query = new StringTemplate("hello " +  
                "$if(param==\"val1\")$" +  
                " it works! " +  
                "$endif$ " +  
                "world");  
        query.setAttribute("param", "val1");  
        System.out.println("result: "+query.toString());

It throws

eval tree parse error :0:0: unexpected end of subtree at org.antlr.stringtemplate.language.ActionEvaluator.ifCondition(ActionEvaluator.java:815) at org.antlr.stringtemplate.language.ConditionalExpr.write(ConditionalExpr.java:99)

score 12 · Accepted Answer · answered Nov 16 '10 at 16:05

12

ST doesn't allow computation in the templates. That would make it part of the model.

answered Nov 16 '10 at 16:05

Terence Parr

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2

It seriously boggles my mind how people can find StringTemplate, read enough about it to create a sample example, yet not grasp its single most important strength. – I82Much Nov 17 '10 at 18:47
6

It's hard to say whether it's really strength or weakness. It's easy to see why this isn't so obvious though: other templating engines have it. And check for equality isn't much of a "computation", plus there are conditionals in string template anyway. – mvmn Jul 04 '12 at 11:43
1

conditionals only test presence or absence, not value. huge diff in terms of model-view separation. – Terence Parr Jul 04 '12 at 18:50
"conditionals only test presence or absence, not value" Wrong - they do test boolean conditions for value, not just presence of any boolean value. – mvmn Dec 05 '16 at 12:15
doesn't iterating over a list or map do calculations on the template ( like size) ? – Viraj May 01 '18 at 11:22
The key difference is there is no user-defined computations allowed :) – Terence Parr May 01 '18 at 23:29

mvmn · Answer 2 · 2018-05-03T10:44:45.590

You can't compare strings inside stringtemplate, unfortunately, but you can send a result of such a comparison into template as a parameter:

StringTemplate query = new StringTemplate("hello " +  
                "$if(paramEquals)$" +  
                " it works! " +  
                "$endif$ " +  
                "world");  
        query.setAttribute("paramEquals", param.equals("val1"));  
        System.out.println("result: "+query.toString());

It might not be what you're looking for, since every time you need to add a comparison you have to pass an extra parameter, and for loops it's even worse. But this is one workaround that may work for simple cases.

Stringtemplate compare strings does not work

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