Golang set struct field using reflect

Question

I am currently doing the following

func Test(controller interface{}) {
    controllerType := reflect.TypeOf(controller)
    controllerFunc := reflect.ValueOf(controller)
    controllerStruct := reflect.New(controllerType.In(0))
    for i := 0; i < controllerStruct.Elem().NumField(); i++ {
        if controllerStruct.Elem().Field(i).Kind().String() == "ptr" {
            controllerStruct.Elem().Field(i).Set(
                reflect.New(
                    controllerStruct.Elem().Field(i).Type(),
                ).Elem(),
            )
        }
    }
    controllerFunc.Call([]reflect.Value{
        controllerStruct.Elem(),
    })
}

Using the following function call

Test(controllers.Test.IsWorking)

type Test struct {
    Name string
    H    *Hello
}

type Hello struct {
    Friend string
}

func (t Test) IsWorking() {
    log.Println(t.H)
}

t.H is always nil even tho I am setting it on the for loop. Also I am not sure if this is the correct way to make this since what about if Hello struct contains another pointer to a struct. Is there a better method to achieve what I am trying to do and why is t.H nil if I am setting it up

Toni Villena · Accepted Answer · 2016-07-27 11:44:19Z

2

t.H is nil because you are giving an incorrect value in Set method. You are getting Value of reflect.New's return (reflect.New(...).Elem() is Hello type, no *Hello type and type of H field is *Hello type). If you change the type of Hfield to Hello type, you will see that it is initialized okay Then, you should do this:

controllerStruct.Elem().Field(i).Set(
    reflect.New(
        controllerStruct.Elem().Field(i).Type().Elem(),
    ),
)

Value of reflect.New(controllerStruct.Elem().Field(i).Type().Elem()) is a new *Hello struct.

I hope that it's useful to you! :-)

answered Jul 27, 2016 at 11:44

Toni Villena

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