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Build Status codecov GitHub release License

Initialize structs with default values

  • Supports almost all kind of types
    • Scalar types
      • int/8/16/32/64, uint/8/16/32/64, float32/64
      • uintptr, bool, string
    • Complex types
      • map, slice, struct
    • Aliased types
      • time.Duration
      • e.g., type Enum string
    • Pointer types
      • e.g., *SampleStruct, *int
  • Recursively initializes fields in a struct
  • Dynamically sets default values by defaults.Setter interface
  • Preserves non-initial values from being reset with a default value


type Gender string

type Sample struct {
	Name   string `default:"John Smith"`
	Age    int    `default:"27"`
	Gender Gender `default:"m"`

	Slice       []string       `default:"[]"`
	SliceByJSON []int          `default:"[1, 2, 3]"` // Supports JSON
	Map         map[string]int `default:"{}"`
	MapByJSON   map[string]int `default:"{\"foo\": 123}"`

	Struct    OtherStruct  `default:"{}"`
	StructPtr *OtherStruct `default:"{\"Foo\": 123}"`

	NoTag  OtherStruct               // Recurses into a nested struct by default
	OptOut OtherStruct `default:"-"` // Opt-out

type OtherStruct struct {
	Hello  string `default:"world"` // Tags in a nested struct also work
	Foo    int    `default:"-"`
	Random int    `default:"-"`

// SetDefaults implements defaults.Setter interface
func (s *OtherStruct) SetDefaults() {
	if defaults.CanUpdate(s.Random) { // Check if it's a zero value (recommended)
		s.Random = rand.Int() // Set a dynamic value
obj := &Sample{}
if err := defaults.Set(obj); err != nil {
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