Freemarker function string formattting - freemarker

Question

I have the issue related to string formatting in a function of the freemarker. Let's admit there is the next function:
<#function transformWithSign sign amount>
<#--<#local str = amount?string["########.00"]>-->
<#local str = amount?string>
<#local str += sign?string>
<#return str>
</#function>
So, the commented out line does not work and appears the error is "freemarker.core.NonMethodException: For "...(...)" callee: Expected a method or function, but this has evaluated to a string (wrapper: f.t.SimpleScalar):
==> amount?string [in template "html/invoiceTemplate.ftlh" at line 52, column 23]"
This row works fine:
<#local str = amount?string>
What is wrong there? Or does the freemarker function not work with string formatting?

Answer 1

The problem is that amount is not a number, but a string that looks like a number. Thus, amount?string will just return the original string as is, and that string doesn't support the [] or () operators. If amount was a number (or date, or boolean), then ?string returns a more fancy string that does support those operators.
To demonstrate the problem:
<#assign amount = 123>
<#-- Works: -->
${amount?string}
<#-- Also works: -->
${amount?string["########.00"]}
But (note the quotation marks around 123):
<#assign amount = "123">
<#-- Works: -->
${amount?string}
<#-- FAILS: -->
${amount?string["########.00"]}
Ideally, you should ensure that amount comes as a number. But, you can also ask FreeMarker to convert it if it's a string, although, be sure that the string in amount uses the typical computer language number format (not some localized format):
${amount?number?string["########.00"]}