有没有一种有效的方法来连接golang模板中的字符串

For example, there is a function like that:

 func TestFunc(str string) string {
 return strings.Trim(str," ")
 }

It runs in the example below:

 {{ $var := printf "%s%s" "x" "y" }}
 {{ TestFunc $var }}

Is there anyway to concatenate strings with operators in template ?

 {{ $var := "y" }}
 {{ TestFunc "x" + $var }}

or

 {{ $var := "y" }}
 {{ TestFunc "x" + {$var} }}

It gives unexpected "+" in operand error.

I couldnt find it in documentation (https://golang.org/pkg/text/template/)