defaults
Initialize structs with default values
- Supports almost all kind of types
- Scalar types
int/8/16/32/64,uint/8/16/32/64,float32/64uintptr,bool,string
- Complex types
map,slice,struct
- Nested types
map[K1]map[K2]Struct,[]map[K1]Struct[]
- Aliased types
time.Duration- e.g.,
type Enum string
- Pointer types
- e.g.,
*SampleStruct,*int
- e.g.,
- Scalar types
- Recursively initializes fields in a struct
- Dynamically sets default values by
defaults.Setterinterface - Preserves non-initial values from being reset with a default value
Usage
package main
import (
"encoding/json"
"fmt"
"math/rand"
"github.com/creasty/defaults"
)
type Gender string
type Sample struct {
Name string `default:"John Smith"`
Age int `default:"27"`
Gender Gender `default:"m"`
Working bool `default:"true"`
SliceInt []int `default:"[1, 2, 3]"`
SlicePtr []*int `default:"[1, 2, 3]"`
SliceString []string `default:"[\"a\", \"b\"]"`
MapNull map[string]int `default:"{}"`
Map map[string]int `default:"{\"key1\": 123}"`
MapOfStruct map[string]OtherStruct `default:"{\"Key2\": {\"Foo\":123}}"`
MapOfPtrStruct map[string]*OtherStruct `default:"{\"Key3\": {\"Foo\":123}}"`
MapOfStructWithTag map[string]OtherStruct `default:"{\"Key4\": {\"Foo\":123}}"`
Struct OtherStruct `default:"{\"Foo\": 123}"`
StructPtr *OtherStruct `default:"{\"Foo\": 123}"`
NoTag OtherStruct // Recurses into a nested struct by default
NoOption OtherStruct `default:"-"` // no option
}
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
}
}
func main() {
obj := &Sample{}
if err := defaults.Set(obj); err != nil {
panic(err)
}
out, err := json.MarshalIndent(obj, "", " ")
if err != nil {
panic(err)
}
fmt.Println(string(out))
// Output:
// {
// "Name": "John Smith",
// "Age": 27,
// "Gender": "m",
// "Working": true,
// "SliceInt": [
// 1,
// 2,
// 3
// ],
// "SlicePtr": [
// 1,
// 2,
// 3
// ],
// "SliceString": [
// "a",
// "b"
// ],
// "MapNull": {},
// "Map": {
// "key1": 123
// },
// "MapOfStruct": {
// "Key2": {
// "Hello": "world",
// "Foo": 123,
// "Random": 5577006791947779410
// }
// },
// "MapOfPtrStruct": {
// "Key3": {
// "Hello": "world",
// "Foo": 123,
// "Random": 8674665223082153551
// }
// },
// "MapOfStructWithTag": {
// "Key4": {
// "Hello": "world",
// "Foo": 123,
// "Random": 6129484611666145821
// }
// },
// "Struct": {
// "Hello": "world",
// "Foo": 123,
// "Random": 4037200794235010051
// },
// "StructPtr": {
// "Hello": "world",
// "Foo": 123,
// "Random": 3916589616287113937
// },
// "NoTag": {
// "Hello": "world",
// "Foo": 0,
// "Random": 6334824724549167320
// },
// "NoOption": {
// "Hello": "",
// "Foo": 0,
// "Random": 0
// }
// }
}