Golang. How to create loop function using html/template package

Question

I'm trying to implement loop as custom function. It takes number of iterations and content between curly brackets, then it should iterate content between brackets n times. Please, see example:

main.go

template.Must(template.ParseFiles("palette.html")).Funcs(template.FuncMap{
        "loop": func(n int, content string) string {
            var r string
            for i := 0; i <= n; i++ {
                r += content
            }
            return r
        },
    }).ExecuteTemplate(rw, index, nil)

index.html

{{define "index"}}
<div class="row -flex palette">
  {{loop 16}}
    <div class="col-2"></div>
  {{end}}
</div>
{{end}}

Output

<div class="row -flex palette">
    <div class="col-2"></div>
    <div class="col-2"></div>
    <div class="col-2"></div>
    <div class="col-2"></div>
    ... 16 times
</div>

Is it possible to implement it? The motivation is that standard functionality of the text/template doesn't allow just to iterate content between curly bracket. Yes we can do it by range action going through "outside" data.

Innominate · Accepted Answer · 2015-03-08 17:13:38Z

12

You can use range on a function that returns a slice. http://play.golang.org/p/FCuLkEHaZn

package main

import (
    "html/template"
    "os"
)

func main() {
    html := `
<div class="row -flex palette">
  {{range loop 16}}
    <div class="col-2"></div>
  {{end}}
</div>`
    tmpl := template.Must(template.New("test").Funcs(template.FuncMap{
        "loop": func(n int) []struct{} {
            return make([]struct{}, n)
        },
    }).Parse(html))
    tmpl.Execute(os.Stdout, nil)
}

edited Mar 8, 2015 at 17:13

answered Mar 7, 2015 at 18:14

Innominate

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3 Comments

Timur Fayzrakhmanov Over a year ago

Good idea! Thus there is no way to get content from curly brackets?)

Logiraptor Over a year ago

If you aren't using the slice elements, it is more efficient to use an empty struct. play.golang.org/p/_jRV62bOB3 This way you only allocate a slice header (constant size) instead of n elements.

Timur Fayzrakhmanov Over a year ago

yeap! you are absolutely right!) @Innominate, please update your answer.

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