去模板删除范围循环中的最后一个逗号

Question

I have code like this:

package main

import (
    "text/template"
    "os"
)

func main() {
    type Map map[string]string
    m := Map {
        "a": "b",
        "c": "d",
    }
    const temp = `{{range $key, $value := $}}key:{{$key}} value:{{$value}},{{end}}`
    t := template.Must(template.New("example").Parse(temp))
    t.Execute(os.Stdout, m)
}

it will output :

key:a value:b,key:c value:d,

but I want something like this:

key:a value:b,key:c value:d

I don't need the last comma, how to remove it. I found a solution for looping an array here: https://groups.google.com/d/msg/golang-nuts/XBScetK-guk/Bh7ZFz6R3wQJ , but I can't get index for a map.

Answer 1

Here's how to write comma separated key-value pairs using a template function.

Declare a function that returns a function that increments and returns a counter:

func counter() func() int {
    i := -1
    return func() int {
        i++
        return i
    }
}

Add this function to the template:

t := template.Must(template.New("example").Funcs(template.FuncMap{"counter": counter}).Parse(temp))

Use it in the template like this:

    {{$c := counter}}{{range $key, $value := $}}{{if call $c}}, {{end}}key:{{$key}} value:{{$value}}{{end}}

This template writes the separators before the key-value pairs instead after the pairs.

The counter is created before the loop and incremented on each iteration through the loop. The separator is not written the first time through the loop.

Run it in the playground.