Text Templates
html/template os strings text/templateGo offers built-in support for creating dynamic content or showing customized output to the user with the text/template package. A sibling package named html/template provides the same API but has additional security features and should be used for generating HTML.
package main
import (
htmltemplate "html/template"
"os"
"strings"
"text/template"
)
func main() {We can create a new template and parse its body from a string. Templates are a mix of static text and "actions" enclosed in {{...}} that are used to dynamically insert content.
t1 := template.New("t1")
t1, err := t1.Parse("Value is {{.}}\n")
if err != nil {
panic(err)
}Alternatively, we can use the template.Must function to panic in case Parse returns an error. This is especially useful for templates initialized in the global scope.
t1 = template.Must(t1.Parse("Value: {{.}}\n"))By "executing" the template we generate its text with specific values for its actions. The {{.}} action is replaced by the value passed as a parameter to Execute.
t1.Execute(os.Stdout, "some text")
t1.Execute(os.Stdout, 5)
t1.Execute(os.Stdout, []string{
"Go",
"Rust",
"C++",
"C#",
})Helper function we'll use below.
Create := func(name, t string) *template.Template {
return template.Must(template.New(name).Parse(t))
}If the data is a struct we can use the {{.FieldName}} action to access its fields. The fields should be exported to be accessible when a template is executing.
t2 := Create("t2", "Name: {{.Name}}\n")
t2.Execute(os.Stdout, struct {
Name string
}{"Jane Doe"})The same applies to maps; with maps there is no restriction on the case of key names.
t2.Execute(os.Stdout, map[string]string{
"Name": "Mickey Mouse",
})if/else provide conditional execution for templates. A value is considered false if it's the default value of a type, such as 0, an empty string, nil pointer, etc. This sample demonstrates another feature of templates: using - in actions to trim whitespace.
t3 := Create("t3",
"{{if . -}} yes {{else -}} no {{end}}\n")
t3.Execute(os.Stdout, "not empty")
t3.Execute(os.Stdout, "")range blocks let us loop through slices, arrays, maps or channels. Inside the range block {{.}} is set to the current item of the iteration.
t4 := Create("t4",
"Range: {{range .}}{{.}} {{end}}\n")
t4.Execute(os.Stdout,
[]string{
"Go",
"Rust",
"C++",
"C#",
})Funcs adds custom functions, and | pipes a value into a function.
t5 := template.Must(template.New("t5").
Funcs(template.FuncMap{"upper": strings.ToUpper}).
Parse("{{.Name | upper}} has {{len .Langs}} languages\n"))
t5.Execute(os.Stdout, map[string]any{"Name": "tuck", "Langs": []string{"go", "sql"}})text/template inserts a value as it is. html/template uses the same actions and escapes the value so the result is safe to serve as HTML.
raw := template.Must(template.New("raw").Parse("text: {{.}}\n"))
raw.Execute(os.Stdout, "<b>")
page := htmltemplate.Must(htmltemplate.New("page").Parse("html: {{.}}\n"))
page.Execute(os.Stdout, "<b>")
}$ go run ./56_text_templates Value: some text Value: 5 Value: [Go Rust C++ C#] Name: Jane Doe Name: Mickey Mouse yes no Range: Go Rust C++ C# TUCK has 2 languages text: <b> html: <b>