Use Go’s standard-library text/template package when formatted output is text rather than HTML: email messages and generated Go source are two examples. It substitutes data into a template without html/template’s context-aware escaping. For HTML output, prefer html/template, which builds on text/template and adds HTML-specific handling. section 9.1 section 9.2 section 13.3
Render an email into a buffer
Parse the template, execute it with message data, then give the buffer’s contents to mail-sending code: package main import ( "bytes" "fmt" "text/template" ) func main() { const body = "From: {{.From}}\nTo: {{.To}}\nSubject: {{.Subject}}\n\n{{.Body}}\n" message := struct{ From, To, Subject, Body string }{ "me@example.com", "you@example.com", "Hello", "Welcome!", } t := template.Must(template.New("email").Parse(body)) var output bytes.Buffer if err := t.Execute(&output, message); err != nil { panic(err) } fmt.Print(output.String()) } The buffer separates rendering from delivery; net/smtp can send the rendered message. Injected properties are not HTML-escaped, so apply escaping explicitly where the output requires it. section 9.2 section 13.3
The same substitution pattern can remove repetitive source-code boilerplate. A queue generator fills package and type names into a Go-source template, then writes one file per requested type. A go:generate directive can invoke that generator. Parse once before producing multiple files rather than repeating the parsing work. section 13.3 section 9.3
Listing 13.19 The queue template
package main
import (
"fmt"
"os"
"strings"
"text/template"
)
var tpl = `package {{.Package}} #1
type {{.MyType}}Queue struct { #2
q []{{.MyType}}
}
func New{{.MyType}}Queue() *{{.MyType}}Queue {
return &{{.MyType}}Queue{
q: []{{.MyType}}{},
}
}
func (o *{{.MyType}}Queue) Insert(v {{.MyType}}) {
o.q = append(o.q, v)
}
func (o *{{.MyType}}Queue) Remove() {{.MyType}} {
if len(o.q) == 0 {
panic("Oops.")
}
first := o.q[0]
o.q = o.q[1:]
return first
}
The queue template shows how package and type-name substitutions turn one implementation pattern into type-specific Go source. section 13.3
For reusable HTML page sections, use html/template rather than switching to text/template: nested templates and shared base templates retain HTML-aware rendering. Templates can also be parsed ahead of use, while buffering output helps avoid partial renderings when execution fails. section 9.1.5 section 9.3
