Go by Example: Text Templates
|
Go offers built-in support for creating dynamic content or showing customized output to the user called Template. |
|
 
package main |
|
|
Go has two template packages. one is “text/template” for regular text manipulation, and another one is “html/template” which has the same API as “text/template” but has additional security features. It should be used when generating HTML. |
import ( "log" "os" "text/template" ) |
func main() { |
|
|
New creates a template with a specific name and returns a pointer to it. |
t1 := template.New("t1")
|
|
Parse parses its parameter as template body. We use {{.}} to access the value passed to the template when it’s getting executed. |
t1, err := t1.Parse("Value is {{.}}\n")
if err != nil {
log.Fatal(err)
}
|
|
If we want to ignore the errors we can use Must function. It will panic if an error occurs when parsing the template. |
t1 = template.Must(t1.Parse("Value is {{.}}\n"))
|
|
Execute applies parsed template to the data we pass to it and writes the output to the io.Writer. |
t1.Execute(os.Stdout, t1.Name())
t1.Execute(os.Stdout, "some text")
t1.Execute(os.Stdout, true)
t1.Execute(os.Stdout, 5)
t1.Execute(os.Stdout, []string{
"Go",
"Rust",
"C++",
"C#",
})
t1.Execute(os.Stdout, struct{ name string }{
name: "Jane Doe",
})
|
|
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 template is executing. |
t2, _ := template.
New("t2").
Parse("Fullname: {{.Fullname}}\n")
|
t2.Execute(os.Stdout, struct { Fullname string }{ Fullname: "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{
"Fullname": "Mickey Mouse",
})
|
|
You can use if control structure to show data conditionally. The data between if block will be shown if the field is truthy. Means it is not false boolean, empty string, nil or zero length slice, nil map/pointer. |
t3, _ := template.
New("t3").
Parse(`{{if .Field1}}
If block => {{.Field1}}
{{ else if .Field2}}
Else if block => {{.Field2}}
{{ else }}
Else block
{{ end }}`)
|
s := struct { Field1 string Field2 []string }{} |
|
s.Field1 = "" s.Field2 = []string{} t3.Execute(os.Stdout, s) |
|
s.Field1 = "Some text" s.Field2 = nil t3.Execute(os.Stdout, s) |
|
|
Using a range action you can loop through a slice. Each time the range block is getting executed dot will be set to current item of slice. |
t4, _ := template.
New("t4").
Parse(`Range: {{ range . }}
{{.}}
{{ end }}`)
t4.Execute(os.Stdout,
[]string{
"Go",
"Rust",
"C++",
"C#",
})
|
|
You can assign and reassign a value to a variable in templates. |
t5, _ := template.
New("t5").
Parse(`Variables: {{ $language := "go" }}
{{ $language }}
{{ $language = "C" }}
{{ $language }}`)
t5.Execute(os.Stdout, nil)
}
|
$ go run templates.go Value is my-template Value is some text Value is true Value is 5 Value is [Go Rust C++ C#] Value is {Jane Doe} Fullname: Jane Doe Fullname: Mickey Mouse |
|
Else block
|
|
Else if block => Some text Range: Go |
|
Rust
|
|
C++
|
|
C# Variables: go C |
Next example: JSON.