defaults

Initialize members in a struct with a default value

• 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

Usage

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 format
	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 even without a tag
	OptOut OtherStruct `default:"-"` // Opt-out
}

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

// SetDefaults implements defaults.Setter interface
func (s *OtherStruct) SetDefaults() {
	if (defaults.CanUpdate(s.Random)) { // Check if the value is initial (recommended)
		s.Random = rand.Int() // Set a value dynamically
	}
}

obj := &Sample{}
if err := defaults.Set(obj); err != nil {
	panic(err)
}