Go Template Syntax

Overview

Go's text/template package provides a powerful and flexible way to generate text output. The following are the basic syntax rules for using text/template:

• Template Definition: Templates are usually defined in .tmpl or .tpl files.
• Actions: Actions are enclosed by {{ and }}, used to insert data or execute logic in the template.
• Variables: Variables are accessed using a dot ., for example {{.Name}}.
• Comments: Start with {{/* and end with */}}.

Actions

Actions are core in the template language, enclosed by {{ }}, for example:

{{.}}              // Current object
{{.Field}}         // Field of the current object
{{if .Condition}}  // Conditional statement
  // Execute some operations
{{end}}
{{range .Items}}   // Loop
  {{.}}
{{end}}

Variable Declaration and Assignment

You can declare and assign variables in the template:

{{ $name := "World" }}
Hello, {{ $name }}!

Conditional Statements

The template language supports conditional statements:

{{if .Condition}}
  True
{{else}}
  False
{{end}}

Loops

range can be used to iterate over arrays, slices, maps, etc.:

{{range .Items}}
  Item: {{.}}
{{end}}

Getting Map Key and Value

{{range $key, $val := .Map}}
 print("{{$key}}", "{{$val}}")
{{end}}

Referencing Variables from the Outer Scope

{{range .Services}}
  print("{{.ServiceName}}")
  {{ $serviceName := .ServiceName }}
{{range .Methods}}
  print("{{$serviceName}}") // Here, reference the ServiceName from the outer Service struct in the inner scope
{{end}}
{{end}}

Functions

Predefined or custom functions can be called in templates:

// Define a struct as the data source for the template
type User struct {
    Name  string
    Age   int
    Email string
}

// Custom function example
func getCurrentYear() int {
    return time.Now().Year()
}


func defineTemplate() {
    // Define the template
    tmpl := template.New("example")

    // Add predefined functions
    tmpl = tmpl.Funcs(template.FuncMap{
        "uppercase": strings.ToUpper, // Use a function from the standard library
        "now":       time.Now,
    })

    // Add custom functions
    tmpl = tmpl.Funcs(template.FuncMap{
        "year": getCurrentYear,
    })

    // Define template content
    const tmplText = `
Hello {{.Name}},

Your email is: {{.Email}}
Your age in {{now | year}} will be {{add .Age 1}}.
And here's your name in uppercase: {{uppercase .Name}}
`

 // Parse template content
)

Removing Whitespace and Newlines

In text/template, the purpose of {{- and -}} is to remove whitespace characters around template tags. Specifically, they can remove whitespace characters (such as spaces, newlines) to the left or right of the tag.

{{- range .Items}}
  {{.Name}}
{{- end}}