How can I use for loops effectively in Go templates?

For Loops in Templates

Templates in Go provide a powerful way to generate dynamic content. One common requirement when working with templates is the need for loops. This article explores how to implement for loops within templates.

Using Range with Prepared Array

The simplest way to create a loop in a template is to use the range keyword with a prepared array. For instance, consider the following code:

<code class="go">type Person struct {
    Name string
    Age  int
}

func main() {
    people := []Person{{"John", 30}, {"Mary", 25}}
    tmpl := template.Must(template.New("loop").Parse(`
        {{range .}}
            Name: {{.Name}}
            Age:  {{.Age}}
        {{end}}
    `))
    tmpl.Execute(os.Stdout, people)
}</code>

This template will iterate over the people slice and print the name and age of each person.

Using an External Function

Another approach is to use an external function to create a loop. This can be useful when you need more flexibility or functionality in your loop. For example, the following function can generate a simple for loop:

<code class="go">func For(start, end int) chan int {
    c := make(chan int)
    go func() {
        for i := start; i < end; i++ {
            c <- i
        }
        close(c)
    }()
    return c
}</code>

This function takes a starting and ending point and returns a channel that iterates over each integer in the range. To use this function in a template, you can do the following:

<code class="go">tmpl := template.Must(template.New("loop").Parse(`
        {{range For 0 10}}
            i: {{.}}
        {{end}}
    `))
tmpl.Execute(os.Stdout, nil)</code>

This template will iterate from 0 to 9 and print the value of i for each iteration.

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