How to Efficiently Concatenate Strings in Go Templates?

Efficient String Concatenation in Go Templates

In Go templates, the need often arises to concatenate strings for various purposes. While the strings.Join function is a versatile option, it can be inefficient in certain scenarios. This article explores alternative methods that offer improved performance.

Using the Printf Function

The printf function provides a simple and efficient way to concatenate strings in Go templates. As demonstrated in the question, you can use printf to merge multiple strings into a single result. The following example concatenates the strings "x" and "y" using printf:

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

Combining Template Expressions

Another way to concatenate strings in Go templates is to combine template expressions. This involves writing the individual strings as separate template expressions and then using the " " operator to join them. However, this method requires parentheses to enclose the variables, as shown below:

{{ $var := "x" + "(" + "y" + ")" }}

Extending the Template Library

If you find yourself frequently concatenating strings in Go templates, consider extending the template library with a custom function. This allows you to define a function that handles string concatenation specifically for your template usage. The following example shows how to define a custom TestFunc that concatenates the strings:

<code class="go">func TestFunc(strs ...string) string {
    return strings.Trim(strings.Join(strs, ""), " ")
}</code>

You can then use the TestFunc in your templates as follows:

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

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