mcuadros / go-defaults Goto Github PK

Example:

type Widget struct {
    B []bytes
}

defaults.SetDefaults(&Widget{})

The B field starts out nil, but will be set to an empty byte slice, even though that field has no "default" tag.

Looking at the code, I'm thinking either setDefaultValues should check for the presence of the tag, and skip the field if not present, or setDefaultValue should check the presence of the tag (after the zero value check).

Alternatively, if this was the intended behavior, then perhaps add a default:"-" option to explicitly skip the field? Or a flag in the Filler struct to toggle the behavior? I'd be happy to do a PR.

In v1.1.0, setting default: "1000000000" for time.Duration was equivalent to "1s".

but, In v1.2.0, setting default: "1000000000" for time.Duration is equivalent to "0".

I have made the fixes in this Pull Request. #18
Please check it out as it is a necessary fix for the project I am using.

@mcuadros

I'd love it if this library also handled type pointers, so something like this:

type test struct {
  Name *string `default:"test"`
}

now obviously a string pointer isn't the most useful thing in the world, but handling it generically should allow us to specify nested struct pointers with their own defaults, and then this library would correctly initialize the whole data tree. I've written a little bit of wrapper code to do this myself (which actually doesn't even handle the string pointer case), but I'd love it if this was something the library just did itself:

setDefaults(reflect.ValueOf(test))

[...]

func setDefaults(v reflect.Value) {
  if v.Kind() != reflect.Ptr { return }
  if v.IsNil() {
    if v.CanSet() {
      v.Set(reflect.New(v.Type().Elem()))
    } else {
      return
    }
  }
  if v.Elem().Kind() != reflect.Struct { return }
  defaults.SetDefaults(v.Interface())
  v = v.Elem()

  for i := 0; i < v.NumField(); i++ {
    field := v.Field(i)
    if field.Type().Kind() == reflect.Ptr {
      setDefaults(field)
    }
  }
}

How can I get the default value of one field derived from other fields of same struct, For example:

type User struct {
Name string
FirstName string
LastName string
}
Here the default value of Name will be derived from FirstName and LastName i.e., Name = concat(FirstName,' ',LastName).

Is there any way to achieve this? @mcuadros Let me know

For fields of type time.Duration the documentation suggests that a default of "1m" should be parsed into the appropriate duration (i.e. 1 * time.Minute).
This does not seem to be working.

Defaults are only correctly applied when using numbers only (which are then interpreted as nanoseconds:

import (
	"fmt"
	"time"	
	"github.com/mcuadros/go-defaults"
)

type Foo struct {
	ConnectionTimeout time.Duration `default:"2000000000"`
}

func main() {
	c := &Foo{}
	defaults.SetDefaults(c)
	fmt.Printf("Foo: %+v", c)
}

Output:

Foo: &{ConnectionTimeout:2s}

However:

import (
	"fmt"
	"time"	
	"github.com/mcuadros/go-defaults"
)

type Foo struct {
	ConnectionTimeout time.Duration `default:"20s"`
}

func main() {
	c := &Foo{}
	defaults.SetDefaults(c)
	fmt.Printf("Foo: %+v", c)
}

Output:

Foo: &{ConnectionTimeout:0s}

package main

import (
	"fmt"

	"gopkg.in/mcuadros/go-defaults.v1"
)

func main() {

	foo := &Parent{}
	defaults.SetDefaults(foo)
	fmt.Print(foo)
}

type Child struct {
	Name string
	Age  int `default:"10"`
}

type Parent struct {
	Children []Child
}

output: &{[]}

If you make a field's default value true you can never set it to false. The go-defaults library will always override the false value to be true.

I made a repository with a small self contained example: link.

I don't think there is a way to fix this. Maybe go-defaults could simply ignore any bool fields. Or maybe make a custom bool type for go-defaults which keeps track of if its value has been set.

type Defaults interface {
  Defaults(raw string) (interface{}, error)
}

example

type Duration time.Duration

func (d *Duration) Defaults(raw string) (interface{}, error) {
  return time.ParseDuration(raw)
}