go template example

main.go

package main

import (
	"os"
	"text/template"
	"time"
)

type Todo struct {
	Name        string
	Description string
	CreatedOn   time.Time
}

type templateInput struct {
	State map[string]interface{}
}

func localSum(a, b int) int {
	return a + b
}

func localAddDays(d time.Time, days int) time.Time {
	return d.AddDate(0, 0, days)
}

var funcMap = template.FuncMap{
	"now":     time.Now,
	"sum":     localSum,
	"addDays": localAddDays,
}

// withAddDay addDays(now, 2)
func withAddDays() {

	tmplInput := templateInput{
		map[string]interface{}{
			"days": 2,
		},
	}

	tmpl := `{{now.Day}} until two days: {{ addDays now (index .State "days")}}`

	t, err := template.New("withState").Funcs(funcMap).Parse(tmpl)
	if err != nil {
		panic(err)
	}

	err = t.Execute(os.Stdout, tmplInput)
	if err != nil {
		panic(err)
	}

}

// withComposition sum(sum(a,b), c)
func withComposition() {

	tmplInput := templateInput{
		map[string]interface{}{
			"a": 1,
			"b": 2,
			"c": 3,
			"d": "something wrong",
		},
	}

	tmpl := `{{now.Year}} sum(sum(a,b),c): {{ sum (sum (index .State "a") (index .State "b") ) (index .State "c")}}`

	t, err := template.New("withState").Funcs(funcMap).Parse(tmpl)
	if err != nil {
		panic(err)
	}

	err = t.Execute(os.Stdout, tmplInput)
	if err != nil {
		panic(err)
	}

}

func withMapState() {

	state := map[string]interface{}{
		"age":  10,
		"name": "bob",
	}
	tmplInput := templateInput{
		state,
	}

	tmpl := `{{now.Year}} {{index .State "name"}} {{ index .State "age"}}`

	t, err := template.New("withState").Funcs(funcMap).Parse(tmpl)
	if err != nil {
		panic(err)
	}

	err = t.Execute(os.Stdout, tmplInput)
	if err != nil {
		panic(err)
	}

}

func withFunction() {

	td := Todo{
		"Test templates",
		"let's test a template to see the magic.",
		time.Now(),
	}

	tmpl := `[{{now.UTC.Year}}][{{ .CreatedOn.Format "02-Jan-2006" }}] You have a task [{{.Name}}] description [{{.Description}}]`

	t, err := template.New("todos").Funcs(funcMap).Parse(tmpl)

	if err != nil {
		panic(err)
	}

	err = t.Execute(os.Stdout, td)
	if err != nil {
		panic(err)
	}
}

func main() {
	//withFunction()
	//withMapState()
	//withComposition()
	withAddDays()
}